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THE 
WATTHOUR  METER 


BY 

WILLIAM  M.  SHEPARD 

'! 

AND 

ALLEN  G.  JONES 


TECHNICAL  PUBLISHING  COMPANY 

604  MISSION  STREET.  SAN  FRANCISCO 
1910 


Copyright  1910 

BY 

TECHNICAL  PUBLISHING 
COMPANY 


P  R  E  F  A  C  K 

Considerable  information  may  be  derived  from 
various  sources  relative  to  the  watthour  meter.  Real- 
izing the  desirability  and  advantage  of  collecting  and 
publishing  such  information  in  concrete  form,  the 
authors  have  endeavored  to  describe  the  prominent 
types  and  the  best  usage  of  modern  domestic  watt- 
hour  meters. 

It  has  been  the  intention  to  prepare  the  facts  in  a 
form  which  will  impart  to  the  central  station  manager, 
the  practical  meter  man  and  to  the  student  alike,  in- 
formation which  will  be  edifying  and  serviceable  for 
reference  and  as  a  guide  for  the  proper  installation, 
connection,  testing  and  maintenance  of  that  most  vital 
factor  in  the  distributing  system — the  watthour  meter. 

Especial  attention  has  been  given  the  induction 
type  and  a  brief  but  concise  explanation  of  its  theory 
and  operation  has  been  made  without  the  use  of  higher 
mathematics.  Maintenance  and  testing  are  also  treated 
in  detail  with  the  dominant  idea  of  giving  the  practical 
man  assistance  in  modern,  effective  and  quick  methods 
of  obtaining  efficient  results.  Comprehensive  tables 
of  testing  constants  and  formula  are  incorporated  in 
Chapter  VIII. 

Where  specific  make  of  meters  is  mentioned,  such 
reference  should  not  be  construed  as  indicating  the 
superiority  of  that  particular  type  over  others,  but 


iv  PREFACE 

should  be  considered  from  the  view-point  of  uniformity 
of  nomenclature  in  order  that  comparisons  may  be 
made  briefly  and  intelligently. 

In  preparing  the  contents  of  this  book,  the  details 
of  electrical  design  have  been  intentionally  omitted. 
The  authors  did  not  feel  that  those  interested  in  the 
general  and  practical  phases  of  the  subject  would 
desire  to  go  deeply  into  such  matters. 

It  has  been  the  urgent  endeavor  to  cover  the  field 
thoroughly.  Supplementary  information  pertinent  to 
the  subject  will  be  gladly  furnished  by  addressing  the 
authors  in  care  of  the  publishers  of  this  book. 

We  desire  to  avail  ourselves  of  the  opportunity  to 
thank  manufacturers  of  meters  referred  to  in  this  pub- 
lication for  their  generous  and  able  co-operation.  We 
are  also  indebted  to  Mr.  F.  G.  Vaughen,  Mr.  O.  A. 
Knopp  and  Mr.  F.  E.  Geibel  and  others  for  their 
liberal  advice  and  assistance. 

THE  AUTHORS. 

San  Francisco,  June,  1910 


TABLE  OF  CONTENTS 

CHAPTER  I 

GENERAL 

PAGE 

Relation  of  the  Meter  to  the  Central  Station  1 

The    Selection    of    Meters    3 

Factors  Affecting  the  Meter's  Accuracy  3 

General    Construction     7 

CHAPTER  II 
MEASUREMENT  OF  POWER 

Graphical  Representation  of  Alternating  Currents    15 

Connections  of  Indicating  Instruments 18 

Equations  of  Power  in  Alternating  Current  Circuits   17 

CHAPTER  III 
THE  INDUCTION  MKTKR 

Reasons  for  Its  Extensive  Use    24 

Principle  of  Operation   24 

Lagging  for  Low  Power  Factor   28 

Light  Load  Adjustment  33 

Effect  of  Frequency  Variation    39 

Calibration    Curves    42 

Connections  of  Single  Phase  Meters   44 

Determination  of  Power   Factor  by   Means  of  Two   Single 

Phase   Meters    , 55 

Polyphase  Meters — Adjustment  of  Elements  61 

Metering  High   Potential   Circuits    63 

CHAPTER  IV 

THE  COM  MUTATING  METER 

Principle  of  Operation   66 

Comparison  to  a  Shunt  Motor ; 66 

General   Construction    68 

Use  of  Commutating  Meters  on  Alternating  Currents 75 

Three- Wire  Meters   77 

Switchboard   Meters    80 

Connections   .                                                                          83 


vi  TABLE  OF  CONTENTS 

CHAPTER  V. 

MERCURY  FLOTATION  METER 

PAGE 

Principle  of  Operation  87 

Diagrammatic  Illustration  D.  C.  Type    89 

Diagrammatic  Illustration  A.  C.  Type    92 

Ampere  Hour  Meter 93 

Connections 94 

CHAPTER  VI 
MISCELLANEOUS 

The  Prepayment  Meter 96 

Maximum  Demand  Indicators   100 

CHAPTER  VII 
MAINTENANCE  AND  TESTING 

Reading  Meters  and  Keeping  of  Records   107 

Forms  of  Record  Cards  107  to  113 

Installation  of  Meters    114 

Testing  With  Indicating  Instruments   118 

Constants  and  Testing  Formulae   119  to  125 

Testing  With  Rotating  Standard   125 

Testing  With  Phantom   Loads    130 

Knopp  Method  of  Testing 132 

Special  Testing  Set  for  D.  C.  Meters 137 

Shop  Methods  of  Testing  140 

Testing  Polyphase  Meters  144 

The  Use  of  Current  and  Potential  Transformers   145 

Meter  Troubles   150 

CHAPTER  VIII 
RATES 

Commonwealth  Edison  Company,  Chicago 157 

Edison  Illuminating  Company,  Boston  165 

Birmingham  (Alabama)  Railway,  Light  and  Power  Company.  170 

San  Francisco  (California)  Gas  and  Electric  Company 171 

APPENDIX 

Definitions 173 

Determination  of  Temperature  Rise  by  Resistance  Method..  175 
Adjusting    Meters    for    Use    With    Current    and    Potential 

Transformers  .                                                                         .  175 


THE  WATTHOUR  METER 

CHAPTER  I. 
GENERAL. 

Definition. 

The  name  "recording  wattmeter"  or  "integrating 
wattmeter,"  is  often  erroneously  applied.  The  true 
name  for  the  instrument  commonly  used  for  recording 
the  energy  flowing  in  an  electrical  circuit  for  a  certain 
period  of  time  is  the  watt-hour  meter,  since  it  records 
the  product  of  the  watts  and  the  time.  The  "recording 
wattmeter"  in  the  true  sense  of  the  word  is  the  instru- 
ment which  is  ordinarily  known  as  the  graphic,  or 
"curve-drawing  wattmeter/'  which  records  the  watts 
for  any  given  instant  without  taking  into  consideration 
the  time  element. 

Relation  of  the  Meter  to  the  Central  Station. 

The  relation  of  the  meter  and  the  meter  system 
to  the  distributing  station  is  a  factor  of  great  im- 
portance, the  gravity  of  which,  as  a  rule,  is  not  fully 
realized;  especially  is  this  true  with  the  small  and  the 
medium-sized  lighting  and  power  companies.  The  rev- 
enue of  the  distributing  company  depends  on  the  meter 
in  more  ways  than  are  at  first  apparent,and  the  con- 
tinued accuracy  of  its  meters  is  a  matter  materially 
affecting  its  financial  success.  Inaccurate  meters  are 
eventually  detrimental  to  the  interests  of  the  company 
selling  current,  regardless  of  whether  the  meter  runs 
fast  or  slow.  A  fast  meter  furnishes  the  consumer  a 
very  just  cause  for  complaint,  and  when  detected 
usually  reacts  strongly  against  the  company  in  produc- 
ing mistrust  of  its  methods  and  a  general  feeling 
among  its  customers  that  they  are  paying  for  some- 
thing that  they  never  receive.  Such  a  feeling  is  to  be 


2  THE   WATTHOUR   METER 

avoided  by  every  possible  means,  as  it  causes  endless 
complaints  and  in  many  cases  the  loss  of  customers 
with  the  resulting  loss  in  revenue. 

Slow  meters,  of  course,  act  directly  on  the  com- 
pany's revenue,  failing  to  record  the  power  which  is 
actually  being  delivered.  This  is  often  a  very  serious 
source  of  loss,  especially  where  meters  are  operating 
at  light  load  for  a  considerable  portion  of  the  time,  as 
is  almost  always  the  case  under  commercial  conditions. 
It  is  this  inaccuracy  in  meters  at  light  loads  that  con- 
stitutes, in  the  majority  of  cases,  the  chief  source  of 
loss  to  the  distributing  company,  and  especially  is  this 
true  where  there  is  no  attempt  made  to  periodically 
test  the  meters  and  make  any  minor  adjustments  that 
may  be  necessary.  Meters  are  often  installed  under 
conditions  that  are  by  no  means  the  most  favorable 
for  a  delicate  piece  of  apparatus ;  this  however,  is  fre- 
quently unavoidable,  as  the  meter  must  be  installed 
wherever  power  is  sold.  It  is  often  installed  in  places 
which  are  inaccessable,  allowed  to  become  covered  with 
•dust  and  dirt,  and  in  some  cases  it  is  placed  where  it  is 
subjected  to  severe  and  continual  vibrations;  it  is 
usually  then  left  to  take  care  of  itself,  receiving  no  fur- 
ther attention  than  to  be  read  once  a  month.  Under 
such  conditions  it  is  almost  inevitable  that  the  meter 
will  eventually  run  slow,  especially  on  light  loads. 

In  carefully  managed  and  well  designed  direct  cur- 
rent systems,  the  energy  lost  in  line  drop  and  other- 
wise unaccounted  for  between  the  station  bus-bars  and 
the  consumer's  meters  may  be  as  low  as  15  per  cent, 
but  on  alternating  current  systems,  having-  many  small 
transformers  connected  to  the  lines  which  are  contin- 
ually consuming  power  in  the  form  of  core  loss,  and 
with  meters  which  are  poorly  maintained  or  entirely 
neglected,  the  loss  shown  by  the  comparison  of  the 
reading  of  the  station  meters  and  the  consumer's 
meters  may  be  as  high  as  70%.  From  15%  to 
20%  represents  very  good  practice  on  direct  current 
systems,  and  from  20%  to  %3O  on  alternating  current 
systems. 


GENERAL  3 

The  Selection  of  Meters. 

The  selection  of  meters  is  a  question  which  should 
be  thoroughly  investigated.  While  there  are  several 
excellent  makes  of  watt-hour  meters  on  the  American 
market,  there  are  still  others  which  may  be  disastrous 
to  the  revenue  of  the  distributing  company.  It  is  not 
always  the  meter  which  when  new  shows  itself  capa- 
ble of  finer  adjustments  and  consequent  high  initial 
accuracy  that  will  prove  the  most  satisfactory  or  the 
most  accurate  after  a  period  of  service  under  average 
commercial  conditions.  Of  course  initial  accuracy  is 
an  important  factor,  but  it  should  not  be  sought  at 
the  expense  of  continued  accuracy.  The  meter  should 
be  of  as  substantial  and  rugged  construction  as  is  con- 
sistent with  efficient  design.  Such  a  meter  will  prove 
to  be  more  satisfactory  and  will  show  less  error  after 
a  period  of  service  than  will  a  meter  of  more  deli- 
cate construction,  although  when  new  it  can  be  ad- 
justed to  a  finer  degree.  This  question  of  continued 
accuracy  is  of  paramount  importance  and  should 
always  be  borne  in  mind  while  selecting  the  instru- 
ment upon  which  the  revenue  of  the  company  is  to 
depend. 

Factors  Affecting  a  Meter's  Accuracy. 

The  factors  affecting  the  accuracy  of  a  watt-hour 
meter  are  various,  but  the  two  principle  ones  are  fric- 
tion and  the  weakening  of  the  permanent  magnets.  If 
these  two  factors  could  be  eliminated,  a  meter  once 
accurately  adjusted  would  remain  so  indefinitely.  Un- 
fortunately, however,  these  two  factors  do  play  a  very 
serious  part  in  the  performance  of  the  meter,  the  most 
serious  being  friction.  If  the  friction  component  was 
a  constant  quantity  it  could  be  compensated  for  by 
the  light  load  adjustment  device  and  thus  permanently 
eliminated  as  regards  the  meter's  accuracy.  It  has 
been  found  though  that  friction  is  an  extremely  varia- 
ble quantity  and  in  the  case  of  any  motor-meter  it 
may  vary  by  quite  a  large  amount,  even  under  very 
favorable  conditions.  For  this  reason  a  high  value 


4  THE   WATTHOUR    METER 

of  the  torque,  or  turning  effort  is  very  desirable,  since 
with  a  high  torque  the  percentage  of  this  torque  re- 
quired to  overcome  any  increase  in  friction  is  rela- 
tively small,  and  the  percentage  increase  of  effective 
torque  due  to  any  decrease  in  friction  is  also  corres- 
pondingly small.  Thus  it  will  be  seen  that  a  meter 
having  a  high  torque  will  not  suffer  in  accuracy  nearly 
so  much  for  the  same  amount  of  change  in  friction  as 
will  a  meter  of  low  torque.  There  is,  however,  a  value 
for  the  torque,  which  if  exceeded,  will  result  in  poor 
economy,  because  by  increasing  the  losses  a  higher 
value  of  torque  can  be  produced.  It  can  therefore 
be  readily  seen  that  the  design  of  a  meter  should  be 
such  that  this  ratio  of  torque  to  watts  loss  will  be  at 
the  most  economical  point. 

Since  friction  is  the  most  serious  factor  affect- 
ing the  accuracy  of  a  watt-hour  meter,  it  is  essential 
that  every  care  and  precaution  be  taken  both  in  the 
design  and  the  manufacture  to  insure  low  initial  fric- 
tion, and  to  insure  as  far  as  possible  against  changes 
in  friction  after  the  meter  has  been  in  service  for  some 
length  of  time.  Friction  will  develop  in  the  lower 
jewel  bearing,  in  the  upper  bearing  and  in  the  record- 
ing mechanism. 

The  Jewel  Bearing. 

In  order  to  obtain  low  friction  in  the  jewel  bear- 
ing the  revolving  element  should  be  light  in  weight; 
only  the  highest  grade  of  jewels  should  be  used,  and 
they  should  be  carefully  selected  and  ground.  The 
pivots,  or  the  bearing  points,  should  be  of  the  finest 
grain  of  glass-hardened  steel.  It  is  usual  practice  of 
manufacturers  to  mount  the  jewel  on  a  spring  sup- 
port, thus  taking  up  any  sudden  vibrations  and  thereby 
preventing  excessive  pressure  between  the  jewel  and 
the  bearing  point,  therefore  prolonging  the  life  of  each. 
Although  the  actual  weight  supported  by  the  lower 
bearing*  is  small,  the  pressure  between  the  jewel  and 
the  pivot  in  a  meter  is  great,  since  the  actual  contact 
area  is  exceedingly  small,  being  as  it  is,  almost  a 


GENERAL  5 

"point"  contact,  so  that  the  pressure  per  square  inch 
of  contact  reaches  an  extremely  high  value.  It  is  for 
this  reason  that  jewels  of  the  best  quality  and  "glass- 
hardened"  steel  pivots  are  necessary  in  the  construc- 
tion of  the  lower  bearing,  as  any  other  material  would 
quickly  break  down  and  develop  excessive  friction. 
The  otherwise  objectionable  "point"  contact  between 
the  jewel  and  the  pivot  is  necessary  in  order  that  low 
initial  friction  may  be  secured. 

Recording  Mechanism. 

When  properly  and  carefully  made,  the  record- 
ing mechanism  is  not  subject  to  the  variations  in  fric- 
tion which  occur  in  the  bearing,  and  it  can  therefore 
be  much  more  completely  compensated  for  by  means 
of  the  light  load  adjustment  device  of  the  meter.  Only 
machine  cut  gears  should  be  used  in  the  construction 
of  the  recording  mechanism,  and  during  the  course 
of  manufacture  every  precaution  should  be  taken  to 
see  that  the  gears  and  their  bearings  are  in  perfect 
condition  and  free  from  all  burrs ;  even  the  slightest 
burr  or  imperfection  in  the  individual  gears  will  prove 
to  be  a  source  of  friction  variation,  and  as  some  of  the 
gears  move  very  slowly  and  as  friction  variation  would 
only  appear  when  the  imperfect  portion  was  in  mesh, 
the  only  feasible  way  of  detecting  and  preventing  this 
source  of  future  error  in  the  meter  is  by  rigid  factory 
inspection  of  all  parts  which  enter  into  the  construc- 
tion of  the  recording  mechanism. 

Weakening  of  the  Permanent  Magnets. 

The  next  important  factor  affecting  the  contin- 
ued accuracy  of  the  watthour  meter,  and  one  of  a  very 
serious  nature,  is  the  weakening  of  the  permanent  mag- 
nets, often  called  the  "retarding  magnets."  The  only 
insurance  which  the  purchaser  has  against  a  poor 
grade  of  permanent  magnet  is  the  ability  .and  the 
experience  of  the  manufacturer.  It  sometimes  hap- 
pens that  meters,  especially  for  switchboard  service, 
are  installed  where  they  are  subjected  to  the  influence 


6  THE   WATTHOUR    METER 

of  powerful  "stray  fields"  which  may  be  set  up,  due  to 
the  proximity  of  wires  or  bus-bars  carrying  heavy 
currents.  To  nullify  the  effects  of  such  stray  fields  on 
the  retarding  magnets,  some  manufacturers  arrange 
the  magnets  astatically,  that  is,  they  are  placed  so 
that  any  stray  field  which  will  tend  to  weaken  one 
magnet  will  correspondingly  strengthen  another,  and 
vice  versa. 

Creeping. 

Under  the  same  category  as  fast  meters  comes  the 
"creeping"  of  meters.  It  is  sometimes  found  that 
meters  will  run  slowly,  or  "creep"  when  there  is  no 
current  flowing  in  the  series  fields,  the  potential  circuit 
alone,  being  energized.  This  is  due  to  the  light  load 
adjustment  exerting  more  than  enough  torque  to  over- 
come the  friction,  and  may  be  due  to  one  or  more 
causes.  The  light  load  adjustment  may  be  so  set  that 
it  just  compensates  for  the  initial  friction  and  the  meter 
then  installed  where  it  is  subject  to  continual  vibra- 
tion, under  which  condition,  the  "friction  torque"  is 
reduced  and  the  meter  will  creep.  Again,  the  meter 
may  be  on  a  circuit  where  the  voltage  is  above  normal, 
which  will  tend  to  produce  creeping.  As  a  general  rule, 
meters  are  so  adjusted  at  the  factory  as  to  allow  for 
a  range  of  several  per  cent  in  voltage  without  causing 
creeping;  such  practice  is  to  be  recommended,  as  the 
slight  benefit  to  be  derived  from  having  the  friction 
completely  compensated  for  is  more  than  counterbal- 
anced by  the  trouble  due  to  creeping  when  such  fine 
adjustments  are  made. 

Overmetering. 

Another  frequent  and  easily  avoidable  source  of 
loss  to  the  distributing  company  is  "over-metering." 
It  often  happens  that  in  the  case  of  public  buildings, 
theaters  and  other  places  where  there  is  a  large  "con- 
nected" load,  and  where  for  a  greater  part  of  the  time 
only  a  small  part  of  this  connected  load  is  actually  tak- 
ing current,  that  one  large  meter  of  sufficient  capacity 


GENERAL  7 

to  take  care  of  the  entire  installation  is  employed. 
When  this  is  done  the  large  meter  will  operate  the 
majority  of  the  time  on  light  load,  and  for  a  consid- 
erable portion  of  the  time  it  may  be  operating  on  very 
light  loads,  and  since  no  commercial  meter  can  be  re- 
lied upon  to  continuously  record  such  light  loads  with 
the  same  accuracy  as  at  or  near  full  load,  there  will  re- 
sult a  considerable  loss  from  the  practice  of  "over- 
metering."  It  is  often  much  better  to  install  a  smaller 
meter  to  take  care  of  such  loads,  even  at  the  risk  of 
an  occasional  burn-out.  Practically  all  standard  meters 
will  carry  a  considerable  overload  for  short  periods, 
and  will  carry  as  much  or  more  than  25%  overload 
continuously  when  located  in  cool,  dry  places.  It  is 
not  recommended  that  meters  be  worked  at  overloads 
continuously,  but  in  many  instances  it  will  be  economy 
to  have  them  work  at  overloads  during  the  period  of 
maximum  demand.  By  exercising  a  little  judgment  a 
meter  can  be  so  selected  that  it  will  never  be  excess- 
ively overloaded,  but  which  will  be  small  enough  to 
give  a  fair  degree  of  accuracy  during  the  light  load 
period. 

Where  the  ratio  of  the  connected  load  to  the  aver- 
age actual  load  is  large,  it  is  better  to  subdivide  the 
circuits  and  install  two  or  more  meters  than  to  at- 
tempt to  handle  the  entire  load  on  one  meter.  In  this 
way  it  can  be  so  arranged  that  while  there  is  no  dan- 
ger of  a  meter  being  severely  overloaded,  it  will  still 
be  small  enough  to  accurately  record  the  power  during 
the  light  load  period. 

General  Construction. 

The  different  types  of  meters  will  be  dealt  with 
separately  hereafter,  therefore  we  will  take  up  at  this 
point  the  various  parts  which  are  common  to  all  types. 

Frames  and  Covers:  The  supporting  frames  to 
which  the  mechanism  is  secured  should  be  rigidly  con- 
structed from  a  mechanical  standpoint,  and  the  ma- 
terial used  should  be  non-magnetic.  The  covers  should 
be  of  sufficient  rigidity  to  protect  the  meter  from  ordi- 


8 


THE    WATTHOUR    METER 


nary  mechanical  injury,  and  should  also  be  light ;  the 
composition  known  as  "white  metal"  is  a  good  material, 
being  used  either  in  its  natural  finish  or  with  a  coat- 
ing of  dull  black  japan.  In  some  cases  glass  is  used 
for  the  covers  so  that  all  working  parts  of  the  meter 
may  be  superficially  inspected  without  removing  the 


O 


Fig.  1.     Supporting  Lugs  of  Base  Frame. 


cover.  For  switchboard  meters,  glass  is  a  sat- 
isfactory material  for  the  covers,  but  for  ordinary 
house  type  meters  the  metal  covers  are  to  be  recom- 
mended ;  glass  covers,  exposing  all  parts  of  the  interior 
to  view,  may  tend  to  invite  tampering  by  unauthor- 
ized persons.  The  internal  frame  which  actually  sup- 
ports the  bearings  and  other  parts  of  the  meter  proper 


GENERAL  9 

should  also  be  made  of  non-magnetic  material.  In  the 
ordinary  type  of  "commutating"  meter  the  construction 
of  the  internal  frame  is  such  that  when  used  on  alter- 
nating currents  it  is  often  the  case  that  heavy  eddy 
currents  may  be  induced  in  the  frame  by  "the  rapid 
reversals  of  the  "projected"  field.  Such  eddy  currents 
cause  undue  heating,  and  to  obviate  this  some  manu- 
facturers split  the  frame  and  insert  a  piece  of  fibre  or 
other  insulating  material. 

The  base  frame  is  usually  furnished  with  three 
supporting  lugs  as  shown  in  Fig.  i,  the  top  lug  being 
key-holed  and  the  lower  right  hand  one  slotted,  thus 
allowing  the  meter  to  be  rapidly  hung  in  place.  It 
can  then  be  properly  levelled  and  set  and  the  sup- 
porting screws  driven  home. 

The  removable  covers  are  usually  held  in  position 
by  two  or  more  studs  which  are  fastened  to  the  base 
frame  and  which  project  up  through  the  covers ;  wing- 
nuts  having  holes  through  their  bodies,  through  which 
seal  wires  may  be  passed,  are  used  on  the  studs  to 
securely  hold  the  covers  in  place.  The  groove  in  the 
base  frame  into  which  the  covers  fit,  should  be  pro- 
vided with  felt  gaskets  to  exclude  dust,  moisture  and 
insects  from  the  interior  of  the  meter.  The  holes  for 
the  entrance  and  exit  of  service  wires  should  also  be 
provided  with  a  dust  proof  feature,  and  the  dial  win- 
dow should  be  set  in  putty  or  other  suitable  material. 

The  Top  Bearing:  The  top  bearing  of  a  meter  is 
necessarily  simple,  as  it  does  not  have  to  support  any 
weight,  but  simply  acts  as  a  guide  bearing,  and  may 
be  the  same  as  or  similar  to  either  of  the  two  types 
shown  in  Fig.  2. 

The  Shaft:  The  shaft  should  be  made  as  light 
as  is  consistent  with  good  design,  and  is  usually  made 
of  steel  approximately  y%-'m.  in  diameter,  some  manu- 
facturers using  a  solid  shaft,  and  others  a  tubular  form. 
At  the  top  of  the  shaft  is  mounted  the  "worm"  gear 
which  transmits  the  motion  of  the  shaft  to  the  record- 
ing mechanism.  There  are  two  general  methods  of 
constructing  the  worm;  one  consists  of  cutting  it 


10  THE   WATTHOUR    METER 

directly  into  the  steel  shaft,  the  other  method  being 
to  mount  a  worm  of  composition  material  in  the  end 
of  the  shaft.  This  latter  method  possesses  the  ad- 
vantage of  allowing  the  use  of  a  non-rusting  material. 
On  the  lower  extremity  of  the  shaft  is  mounted  the 
removable  pivot. 

Discs:  Until  several  years  ago,  the  meter  discs 
were  made  almost  exclusively  of  copper  on  account 
of  its  high  conductivity,  but  aluminum  has  practically 
superseded  copper  for  this  purpose,  due  to  its  lighter 
weight.  An  aluminum  disc  having  the  same  conduc- 
tivity as  a  copper  disc  will  weigh  only  about  48%  as 


Discs  of  Billiard  Cloth 
•oiked  In  Jewelers  Oil 


Fig.  2.    Types  of  Top  Bearing. 

much  as  the  copper.  Therefore  the  aluminum,  though 
of  greater  thickness,  is  much  more  desirable.  The 
question  is  often  asked :  "Why  are  most  meter  discs 
roughened  or  covered  with  little  holes  which  resemble 
prick-punch  marks?"  This  has  nothing  whatever  to 
do  with  the  electrical  characteristics  of  the  meter,  as 
is  sometimes  supposed,  but  simply  results  from  a  fac- 
tory method  of  producing  a  plane  surface.  The  disc 
is  placed  on  a  heavy  metal  block,  and  a  weight  having 
a  roughened  surface  is  allowed  to  fall  upon  the  disc, 
thus  producing  the  peculiar  marking.  It  has  been 
found  that  this  process  eliminates  any  trouble  which 
may  be  due  to  the  warping  of  the  disc. 

The  Lower  Bearing:  There  are  at  the  present 
time  two  general  types  of  lower  bearings  in  use ;  the 
pivot  and  jewel  type  as  shown  in  Fig.  3,  and  the  ball 
and  jewel  type  as  shown  in  Fig.  4.  The  ball  bearing 


GENERAL 


11 


is  relatively  a  new  departure,  but  in  reality  it  is  essen- 
tially a  "pivot"  bearing  also,  and  as  far  as  the  com- 
parative friction  is  concerned,  they  are,  it  is  safe  to 
say,  about  equal.  So  long  as  the  ball  remains  perfectly 
smooth  and  free  from  rus+  it  serves  its  purpose  ad- 
mirably. 


Fig.  3.      Pivot  and  Jewel  Type  of  Lower  Bearing. 

Jewels:  It  has  been  found  that  there  are  but 
two  kinds  of  jewels  which  are  satisfactory  for  use  in 
the  lower  bearings  of  meters,  they  being  the  diamond 
and  the  selected  eastern  sapphire.  In  self-contained 
meters,  up  to  and  including  50  k.  w.  capacity,  the 
sapphire  is  generally  used  to  the  best  advantage ;  above 


12 


THE   WATTHOUR   METER 


this  value,  it  is  advisable  to  use  the  diamond,  because 
of  its  unequalled  hardness.  Where  great  accuracy 
is  desired  in  the  case  of  switchboard  meters  in 
central  stations,  it  is  often  desirable  to  use  diamond 
jewels  in  meters  of  as  small  a  capacity  as  5  amperes. 
In  all  cases,  the  jewel  should  be  carefully  selected, 
ground  and  polished,  and  should  be  free  from  all  flaws. 
It  has  been  noted  that  under  normal  conditions,  the 
average  sapphire  jewel  will  stand  as  much  or  more 
than  600,000  revolutions  of  the  shaft,  and  in  some 


Figr,  4.    Ball  and  Jewel  Type  of  Lower  Bearing. 


cases  the  diamond  jewel  has  lasted  for  as  many  as 
35,000,000  revolutions  of  the  shaft.  These  values,  how- 
ever, are  extremely  variable  and  depend  to  a  great  ex- 
tent upon  the  conditions  and  care  under  which  the 
meter  operates. 

The  Retarding  Magnets:  It  is  of  the  utmost  im- 
portance that  the  strength  of  the  retarding  magnets 
be  as  permanent  as  is  possible  to  make  them,  since 
their  retarding  or  "dragging"  effect  is  proportional 
to  the  square  of  their  magnetic  strength.  Therefore  a 
slight  change  in  the  strength  will  have  an  appreciable 


GENERAL  13 

effect  upon  the  speed  of  the  disc.  Much  depends 
upon  the  physical  properties  of  the  steel  from  which 
the  magnets  are  manufactured,  and  the  most  rigid 
inspection,  by  both  chemical  and  physical  analyses 
should  be  made  of  each  lot  of  steel  before  it  is  treated 
for  use  as  meter  magnets.  The  manufacturer,  after 
he  has  given  the  steel  a  special  process  of  treatment, 
hardens,  forms  and  magnetizes  the  product.  The  com- 
pleted magnet  is  then  subjected  to  hammer  blows  to 
detect  any  mechanical  imperfections,  and  if  it  should 
fail  to  "ring  true"  is  rejected.  It  then  undergoes  an 
artificial  aging  process ;  accurate  measurements  of 
magnetic  strength  being  made  at  frequent  intervals. 
It  is  then  laid  away  for  several  months  after  which 
the  strength  is  again  measured  and  if  this  latter  meas- 
urement differs  in  the  least  from  its  strength  when 
first  laid  away  it  is  discarded. 

A  very  successful  process  of  magnetizing  meter 
magnets  consists  in  slipping  the  completed  form  over 
a  copper  bar,  through  which  a  heavy  current  of  elec- 
tricity (many  thousands  of  amperes)  is  passed  mo- 
mentarily. In  this  way  a  great  number  of  forms  can 
be  magnetized  at  the  same  time,  and  a  uniform 
strength  produced.  Great  care  is  taken  in  the  manu- 
ture  of  the  permanent  magnets,  and  as  a  rule  the  re- 
sults are  very  satisfactory. 

The  Recording  Mechanism :  As  previously  pointed 
out,  the  recording  mechanism  should  be  manufactured 
with  the  greatest  care,  and  rigid  factory  inspection  is 
practically  the  only  safeguard  against  imperfections. 
Meters  are  often  placed  in  such  positions  that  the 
meter  reader  will  encounter  reflected  light,  and  for 
this  reason  it  will  generally  be  found  that  a  dial  of 
unglazed  material  will  be  less  difficult  to  read  under 
all  conditions.  The  recording  mechanism  should  be 
so  constructed  and  provided  with  such  dowel  pins  that 
it  can  be  removed  from  the  meter  at  any  time  and  then 
replaced  in  the  exact  position  from  which  it  was  orig- 
inally taken  without  disturbing  in  the  least  the  mesh  of 
the  worm  with  the  first  gear. 


14  THE    WATTHOUR    METER 

From  the  foregoing  description  of  the  general  con- 
struction, a  very  good  idea  can  be  gathered  as  to  the 
mechanical  requirements  of  a  good  meter;  a  study  of 
the  subsequent  chapters  treat  of  the  electrical  char- 
acteristics. 

There  are  still  to  be  found  throughout  the  coun- 
try a  number  of  the  very  old  type  "low  efficiency" 
meters,  and  a  great  many  of  the  ampere-hour  type ; 
it  is  the  recommendation  of  the  authors  to  replace 
such  old  metors  with  some  make  of  good  modern  watt- 
hour  meter,  as  in  the  majority  of  cases  the  increased 
revenue  to  be  derived  will  pay  many  times  for  the  in- 
terest on  the  cost  of  the  exchange. 


CHAPTER  II. 
THE  MEASUREMENT  OF  POWER. 

The  power  in  a  direct  current  circuit  is  equal  to 
the  product  of  the  electro  motiveforce  and  the  current ; 
in  other  words,  if  I  represents  the  current  in  amperes, 
and  E,  the  e.m.f.  in  volts,  then  the 

El 


Watts,  W  =  El,  or  the  kilowatts 


1000 


Fig.  5. 

The  power  flowing  in  a  direct  current  circuit  can 
therefore  be  determined  by  the  use  of  a  voltmeter  and 
an  ammeter,  or  by  one  instrument,  an  indicating  watt- 
meter, which  will  indicate  the  product  of  the  volts  and 
amperes. 

The  power  flowing  in  an  alternating  current  cir- 
cuit is  dependent  not  only  upon  the  e.m.f.  and  the 
current,  but  also  upon  the  power  factor  of  the  circuit. 
This  is  evident  as  is  illustrated  by  Fig.  5,  which  shows 


16 


THE   WATTHOUR   METER 


a  sine  wave  of  e.m.f  and  current  at  unity  power  fac- 
tor. In  Fig.  6  is  shown  the  same  current  and  e.m.f. 
but  with  a  power  factor  of  50  per  cent  instead  of  unity. 
The  instantaneous  value  of  the  power  flowing  in  any 
circuit  is  equal  to  the  product  of  the  instantaneous 
value  of  the  e.m.f.,  and  the  instantaneous  value  of  the 
current. 

The  curve  P  represents  these  instantaneous  values 
of  the  power.  It  will  be  noted  that  in  the  case  of 
unity  power  factor  (Fig.  5),  the  curve  P  is  entirely 
above  the  axis,  that  is  the  line  of  zero  value ;  this  indi- 
cates that  the  power  is  all  flowing  in  one  direction.  It 


Fig.  6. 


will  also  be  noted  that  the  maximum  value  of  the 
e.  m.  f.  occurs  at  the  same  instant  as  the  maximum 
current,  which  condition  gives  the  maximum  value  of 
the  power  for  these  values  of  the  current  and  the 
e.m.f.,  as  can  be  seen  from  the  figure. 

Referring  to  Fig.  6,  it  will  be  noted  that  for  a 
power  factor  of  50  per  cent,  part  of  the  curve,  P,  ?.s 
below  the  axis,  which  indicates  that  the  power  is  not 
all  flowing  in  the  same  direction,  but  that  during  a 
part  of  the  cycle  a  portion  of  the  power  is  actually 
being  "pumped  back"  into  the  circuit.  The  net  value 
of  the  power  supplied  is  equal  to  the  difference  be- 
tween that  represented  by  the  area  enclosed  by  the 


THE    MEASUREMENT   OF   POWER  17 

curve,  P,  which  is  above  the  axis  and  the  area  en- 
closed by  that  part  of  the  curve  which  is  below  the 
axis.  • 

Assuming  a  sine  wave  of  e.  m.  f.,  and  of  current 
(modern  commercial  alternating  current  generators 
give  waves  closely  approximating  a  sine  wave),  and. 
denoting  the  maximum  value  of  the  e.m.f.  by  E,  the 
maximum  value  of  the  current  by  I,  and  the  instan- 
taneous value  of  the  e.m.f.  by  e,  we  have 

e  =  E  sin  <f>, 

where  <£  =  w  t,  in  which  <o  =  2  ?r  f  (f  being  the  fre- 
quency of  the  circuit  in  cycles  per  second)  and  t  =  the 
time  in  seconds  measured  from  the  instant  when  the 
e.m.f.  crosses  the  axis  in  a  positive  or  rising  direc- 
tion. 

The  instantaneous  value  of  the  current,  i  =  I  sin 
(<f> —  6),  where  6  =  the  angle  of  phase  displacement 
between  the  current  and  the  e.  m.  f.  The  instanta- 
neous power,  p,  is  equal  to  the  product  of  the  in- 
stantaneous e.  m.  f.  and  the  instantaneous  current,  or 

p  =  e  i,  =  E  sin  <f>  I  sin  (<£ — 6) 
or  p  =  El  cos  0  sin  2<£  —  El  sin  6  sin  <f>  cos  <j>. 

Let  P  =  the  average  value  of  p, 

then  P  =  av'g  (El  cos  6  sin  2<£ — El  sin  0  sin  $  cos  <f>) 
=  El  cos  6  (av'g  sin  *<f>)  El  sin  6  av'g  (sin  <f>  cos  <£). 

The  average  value  of  sin  ^  =  ^2,  and  the  aver- 
age value  of  sin  <£  cos  </>  =  O,  substituting  these 
average  values  in  the  above  equation,  we  have 

__  El  cos  6 
2 

But  E,  the  maximum  value  of  the  e.m.f.  wave=V  2  E, 
where  E  is  the  effective  value  of  the  e.m.f.  Also,  if  I 
denotes  the  effective  current,  the  maximum  current, 
I  =  V  2  I-  Therefore,  we  have  the  fundamental  for- 
mula : 


18 


THE   WATTHOUR   METER 


P  =  El  cos  0;  the  cos  0  being  the  power  factor  of 
the  circuit. 

If  the  power  factor  is  unity,  then  cos  0=  i,  and 
hence  the  above  equation  becomes  P  =  El,  which,  as 
will  be  noted,  is  the  same  as  for  direct  current.  The 
power  factor  is  very  seldom  as  high  as  unity,  and  it 
is  therefore  almost  always  necessary  to  use  a  watt- 
meter rather  than  a  voltmeter  and  ammeter;  a  prop- 
erly constructed  arid  accurately  calibrated  wattmeter 


m 

"SET 

B 

1  i  I 

i  1  1 

Sot 


Fig.  7. 


will  measure  power  correctly  regardless  of  the  value, 
of  the  power  factor.  The  power  factor  of  a  single 
phase  alternating  current  can  be  easily  obtained  by 
taking  the  product  of  the  volts  and  the  amperes  as 
indicated  by  a  voltmeter  and  ammeter  and  dividing 
this  result  into  the  actual  power  reading  as  indicated 
by  a  wattmeter. 

The  actuating  force  in  an  indicating  wattmeter 
is  derived  from  two  sets  of  coils,  one  being  connected 
in  multiple,  and  the  other  in  series  (as  in  the  case  of 


THE    MEASUREMENT    OF    POWER 


19 


the  watthour  meter)  with  the  load  to  be  measured. 
The  reaction  between  these  two  coils  is  at  each  instant 
proportional  to  the  instantaneous  values  of  the  current 
and  the  e.  m.  f.,  so  that  the  total  deflecting  force  acting 
on  the  pointer  of  the  instrument  is  at  all  times  propor- 
tional to  the  true  power. 

A  two-phase  system  (often  called  "quarter 
phase"),  can  be  considered  as  two  single  phase  sys- 
tems, and  the  power  being  supplied  by  such  a  system 
is  simply  the  sum  of  the  power  flowing  in  the  two 


Sou  fee 


J_ 

ri   i  i 

—                •- 

£=2 

J 

Fig.  8. 


equivalent  single-phase  systems,  and  can  be  measured 
by  a  single-phase  wattmeter  in  each  system,  or  by  one 
polyphase  wattmeter  as  shown  in  Fig.  7,  in  which 
lines  i  and  3  constitute  one-phase  and  2  and  4  the 
other  phase. 

The  power  in  a  two-phase  three-wire  system  can 
also  be  measured  by  two  single-phase  wattmeters  or 
by  one  polyphase  wattmeter,  the  connections  being 
made  as  shown  in  Fig.  8,  in  which  line  number  2  car- 
ries the  resultant  current.  Fig.  9  shows  the  connec- 
tions used  when  measuring  power  in  a  balanced  two- 


20 


THE   WATTHOUR   METER 


phase  three-wire  system  with  one  single-phase  meter. 
In  this  case  the  voltage  impressed  on  the  meter  will  be 
V  2  or  1.41  times  the  voltage  of  either  phase,  and 
when  the  system  is  balanced  the  current  flowing  in 
the  line,  2,  will  also  be  V  2,  or  1.41  times  the  current 


Scrasce 


Fig.  9. 


Fig.  10. 


Fig.  11. 

in  either  phase.  The  one  wattmeter  method  will  meas- 
ure the  true  power  only  when  the  phases  are  per- 
fectly balanced,  and  is  therefore  very  seldom  used. 

The  power  flowing  in  a  three-phase  system  can 
be  measured  by  two  single-phase  meters  connected 
as  shown  in  Fig.  10,  or  by  one  polyphase  meter  con- 
nected as  shown  in  Fig.  n. 


THE    MEASUREMENT    OF    POWER 


21 


The  power  in  a  three-phase  four-wire  system  can 
be  measured  by  three  single-phase  wattmeters  con- 
nected as  shown  in  Fig.  12;  the  three-phase  four-wire 
system  being  virtually  three  single-phase  systems.  The 


Fig.  12. 

total  power  will  be  the  sum  of  the  indications  of  the 
three  meters.  The  power  in  a  three-phase  four-wire 
system  can  also  be  measured  by  two  single-phase 
meters  connected  as  shown  at  (a)  in  Fig.  13,  or  with 
one  polyphase  meter  in  conjunction  with  current  (or 
series)  transformers  connected  as  shown  at  (b)  in 
Fig.  13- 


Fig.  13a. 


The  power  flowing  in  a  three-phase  system  is  ex- 
pressed by  the  equation,  P  =  V  3  El,  cos  B,  where 
E  is  the  voltage  between  the  phases,  I  the  current 
per  leg  and  cos  (9,  the  power  factor  of  the  circuit, 
When  the  system  is  not  balanced  the  average  values 


22 


THE    WATTHOUR    METER 


of  the  current,  the  voltage  and  the  power  factor  should 
be  used  in  the  above  equation,  remembering'  that  6 
is  the  angular  displacement  between  the  line  current 
and  the  voltage  between  line  and  neutral. 


Fig.  13b. 


Fig.  14  shows  the  method  of  connecting  one  single 
phase  wattmeter  for  measuring  the  power  in  a  bal 
anced  three-phase  three-wire  system. 


Sot/s-ce 


Fig.  14. 

Power  is  the  rate  at  which  energy  is  supplied. 
Electrical  power  is  measured  in  watts  and  kilowatts, 
and  electrical  energy  is  measured  in  watt-hours  and 
kilowatt-hours.  "Purchasers  of  power"  are  in  reality 
purchasers  of  energy,  and  in  order  to  determine  the 
energy  flowing  in  a  circuit  it  is  necessary  that  the 


THE    MEASUREMENT    OF    POWER  23 

power  be  multiplied  by  the  time.  If  w  =  the  power 
in  kilowatts,  and  t  =  the  time  in  hours  during  which 
the  power  is  flowing,  then  the  energy  =  w  t  =  kilo- 
watt-hours. Since  it  is  energy  and  not  power  which 
is  bought,  it  is  necessary  to  have  an  instrument  which 
will  take  into  consideration  the  time  element ;  such 
an  instrument  is  the  watthour  meter. 


CHAPTER  III. 
THE  INDUCTION  METER. 

At  the  present  time  the  induction  type  of  watt- 
hour  meter  is  used  almost  exclusively  where  alternat- 
ing currents  are  concerned,  and  as  alternating  current 
is  much  more  extensively  used  for  general  lighting  and 
power  distribution  than  is  direct  current,  there  are 
considerably  more  induction  meters  being  manufac- 
tured than  there  are  of  any  other  type. 

Reasons  for  Its  Extensive  Use. 

Some  of  the  principle  reasons  for  this  almost  ex- 
clusive use  of  the  induction  meter  on  alternating  cur- 
rent circuits  are  as  follows :  The  induction  meter  is 
more  rugged  in  design,  having  no  brushes,  no  com- 
mutator, or  other  moving  contacts.  The  revolving  ele- 
ment consists  simply  of  the  shaft  and  revolving  disc, 
all  windings  being  on  the  stationary  element. 

The  weight  of  the  moving  element  being  less  than 
that  of  the  commutating  type  of  meter,  and  the  fact 
that  it  has  no  commutator  with  its  resulting  friction, 
necessarily  eliminates  an  appreciable  amount  of  fric- 
tion and  also  results  in  less  jewel  wear. 

For  the  above  reasons,  the  induction  meter  will 
maintain  its  accuracy  better  with  the  same  amount  of 
attention  than  will  other  types  of  "motor"  meters. 

The  induction  meter  is  entirely  free  from  commu- 
tator and  brush  troubles,  having  neither  brushes  nor 
commutator.  It  is  cheaper  in  first  cost  than  any  other 
type  of  meter,  suitable  for  use  on  alternating  currents, 
which  can  compare  with  it  in  continued  accuracy. 

Principle  of  Operation. 

The  induction  meter  consists  essentially  of  the 
stationary  element,  the  rotating  element  (consisting 


THE    INDUCTION    METER 


25 


merely  of  the  shaft  and  disc),  the  recording  mechanism, 
the  jewel  bearing  and  the  retarding  magnets. 

The  stationary  element  consists  of  the  magnetic 
circuit,  A,  Fig.  15,  which  is  built  up  of  laminated  steel 
punchings ;  the  current  coils,  B ;  the  potential  coil,  C ; 
the  light  load  adjustment,  D ;  and  the  lagging  coil,  E. 
The  current  and  potential  coils  are  mounted  as  shown 
in  the  figure,  in  such  a  way  that  the  magnetic  flux  set 


Fig.  15. 


up  by  each  of  these  coils  will  pass  through  the  meter 
disc,  and  this  alternating  flux  passing  through  the  me- 
tallic disc  will  set  up  currents  therein  which  will  flow 
as  indicated  in  Fig.  16,  the  disc  acting  virtually  as 
the  short-circuited  secondary  of  a  transformer.  It  will 
be  seen  from  Fig.  16  that  the  currents  set  up  in  the 
disc  by  the  potential  coil  P  flow  past  the  poles  of  the 
current  coils,  P1,  and  that  the  currents  set  up  by  the 


26 


THE    WATTHOUR    METER 


current  coils  flow  past  the  pole  of  the  potential  coil. 
These  currents  set  up  in  the  disc  are  in  phase  with  the 
voltages  producing  them,  since  the  circuit  offered  by 
the  disc  itself  is  non-inductive.  The  voltages  jn  the  disc 
which  produce  these  currents,  however,  lag  90  degrees 
behind  the  fluxes  set  up  by  the  coils  on  the  stationary 
element,  as  an  induced  voltage  is  always  90  degrees 
behind  the  inducing  flux.  The  flux  is  in  phase  with  the 
current  which  produces  it,  the  angle  of  hysteretic  lag 
being  negligible,  so  that  we  have  currents  flowing  in 
the  disc  lagging  90  degrees  behind  the  currents  flowing 
in  the  meter  windings. 


Fig,   16. 


The  potential  coil  is  wound  with  many  turns  of 
fine  wire,  and  is  therefore  highly  inductive,  so  that  the 
current  flowing  in  this  coil  is  practically  90  degrees  be- 
hind the  impressed  e.m.f,  and  the  flux  from  the  pole 
of  the  potential  coil  is  brought  to  exactly  90  degrees 
behind  the  impressed  e.m.f.  by  use  of  the  lagging  coil, 
as  will  be  explained  later.  The  flux  from  the  poles  of 
the  current  coils  will  be  in  phase  with  the  current,  and 
therefore  in  the  case  of  a  load  of  unity  power  factor 
will  be  in  phase  with  the  impressed  e.m.f.  It  can  be 
readily  seen  from  this  that  in  the  case  of  unity  power 
factor  the  current  set  up  in  the  disc  by  the~~£ptential 
coil  (which  lags  90  degrees  behind  the  flux  from  the 
potential  coil),  will  be  in  phase  with  the  flux  from  the 


THE   INDUCTION    METER  27 

current  coils,  and  also  that  the  current  set  up  in  the 
disc  by  the  current  coils  will  be  in  phase  with  the  flux 
from  the  potential  coil.  It  will  further  be  seen  by 
referring  to  Fig.  16  that  the  disc  currents  set  up  by 
the  potential  coil  will  flow  past  the  center  of  the  cur- 
rent coil  poles,  and  that  the  disc  current  set  up  by  the 
current  coils  will  flow  past  the  center  of  the  potential 
coil  pole.  This  will  give  rise  to  a  mechanical  force 
tending  to  cause  the  disc  to  revolve,  since  any  con- 
ductor carrying  current  at  right  angles  to  a  magnetic 
field  is  subjected  to  a  force  which  tends  to  move  the 
conductor  out  of  such  field.  Furthermore,  this  force 
is  proportional  to  both  the  current  flowing  in  the  disc 
and  to  the  field  strength  or  to  the  product  of  these 
two  factors.  In  the  case  of  the  meter  the  current  flow- 
ing under  the  pole  of  the  potential  coil  is  proportional 
to  the  line  current,  and  the  flux  is  proportional  to  the 
impressed  e.m.f.  Similarly,  the  current  flowing  under 
the  poles  of  the  current  coils  is  proportional  to  the  im- 
pressed e.m.f.  and  the  flux  from  the  current  coil  poles 
is  proportional  to  the  line  current.  The  force  tending 
to  revolve  the  disc  is  therefore  proportional  to  twice 
the  product  of  the  current  and  the  voltage,  or  what  is 
the  same  thing,  it  is  proportional  to  the  product  of  the 
current  and  voltage,  or  to  the  watts. 

The  principle  of  the  induction  meter's  operation 
may  be  explained  in  a  somewhat  different  way,  which 
is  perhaps  more  clearly  understood ;  that  is,  the  electri- 
cal element  may  be  considered  as  the  stator  of  an  in- 
duction motor  and  the  disc  as  the  rotor.  The  "shifting" 
magnetic  field  in  the  case  of  a  meter  (which  corre- 
sponds to  the  "revolving"  magnetic  field  of  the  motor), 
is  supplied  by  the  current  coil  and  the  potential  coil 
poles,  the  flux  from  the  potential  coil  pole  being  90 
degrees  out  of  phase  with  the  flux  from  the  current 
coil  poles,  as  previously  explained.  This  "shifting" 
magnetic  field  sets  up  currents  in  the  meter  disc,  which 
reacting  with  the  magnetic  field  produces  a  force  tend- 
ing to  rotate  the  disc,  exactly  as  the  "revolving"  field 
of  an  induction  motor  sets  up  currents  in  the  rotor, 


28  THE    WATTHOUR    METER 

which  reacting  with  the  "revolving"  magnetic  field  pro- 
duces a  torque  which  causes  the  motor  to  run. 

In  the  case  of  power  factors  which  are  other  than 
unity,  the  flux  produced  by  the  current  coils  (which 
flux  is  in  phase  with  the  current),  will  no  longer  be  90 
degrees  out  of  phase  with  the  flux  from  the  potential 
coil,  but  will  be  90  degrees  plus  or  minus  the  angle  of 
current  displacement  or  the  angle  by  which  the  cur- 
rent is  out -of  phase.  This  being  the  case,  the  disc 
currents  set  up  by  these  coils  will  no  longer  be  in  phase 
with  the  flux  from  the  poles  under  which  they  flow, 
but  will  be  out  of  phase  by  the  angle  of  current  dis- 
placement. The  force  tending  to  turn  the  disc  will 
therefore  no  longer  be  directly  proportional  to  the 
product  of  the  current  and  the  flux,  but  it  will  now  be 
proportional  to  the  product  of  the  current,  the  flux 
and  the  cosine  of  the  angle  of  current  displacement, 
which  is  the  power  factor.  Therefore  the  meter  will 
still  register  the  true  watt-hours. 

Another  way  of  expressing  this  is  to  consider  that 
the  force  acting  on  the  disc  will  be  proportional  to 
the  product  of  the  flux  and  the  component  of  the  disc 
current  which  is  in  phase  with  the  flux.  Since  the  disc 
current  is  out  of  phase  with  the  flux  by  the  angle  of 
current  displacement,  the  component  of  the  disc  cur- 
rent in  phase  with  the  flux  is  equal  to  the  total  disc 
current  multiplied  by  the  cosine  of  the  angle  of  dis- 
placement, or  the  power  factor. 

Lagging  for  Low  Power  Factor. 

In  order  for  the  meter  to  register  correctly  on  low 
.power  factors  it  is  necessary  for  the  flux  from  the  pole 
of  the  potential  coil  to  be  exactly  90  degrees  behind 
the  impressed  e.m.f.  If  the  flux  from  the  potential  pole 
is  less  than  90  degrees  behind  the  impressed  e.m.f.  the 
meter  will  run  slow  on  lagging  and  fast  on  leading  cur- 
rents, while  if  the  flux  lags  more  than  90  degrees  it 
will  run  fast  on  lagging  and  slow  on  leading  currents. 
This  condition  is  obtained  by  a  method  known  as 
lagging,. and  is  accomplished  as  follows:  In  figure  15 


THE   INDUCTION    METER 


29 


C  is  the  potential  coil,  and  E  is  the  lagging  coil  which 
is  mounted  over  the  pole  tip  of  the  potential  coil.  The 
current  in  the  potential  coil  will  be  not  quite  90  degrees 
behind  the  impressed  e.m.f.,  due  to  fhe  RI2  losses  in  the 
winding  and  the  losses  in  the  iron  which  give  rise  to  an 
energy  component  of  the  current.  The  flux  will  be  in 
phase  with  the  current,  and  will  therefore  be  not  quite 
90  degrees  behind  the  impressed  e.m.f.  A  part  of  this 


Fig.  17. 

flux  will  pass  through  the  lagging  coil  and  on  through 
the  meter  disc.  This  flux  induces  an  e.m.f.  in  the  lag- 
ging coil  which  is  90  degrees  behind  it  in  phase.  This 
is  shown  by  the  vector  diagram,  Fig.  17.  In  this 
diagram  OE  represents  the  impressed  e.m.f.  and  OI  the 
current  in  the  potential  coil  which  lags  not  quite  90 
degrees  behind  this  e.m.f.  O<£  represents  the  flux  set 
up  by  the  current,  which  passes  through  the  lagging 


30  THE   WATTHOUR   METER 

coil  and  meter  disc.  This  flux  induces  the  e.m.f.,  OE', 
in  the  lagging  coil,  which  is  90  degrees  behind  it  in 
phase.  The  circuit  of  the  lagging  coil  is  closed  through 
a  resistance,  the  amount  of  which  can  be  varied  and 
therefore  the  amount  of  current  flowing  in  this  circuit 
can  be  varied.  This  current  is  represented  in  the 
diagram  by  OI'.  The  current  OF  will  set  up  a  flux  O^> 
in  phase  with  itself,  and  this  will  combine  with  the 
flux  O<£,  producing  the  resultant  flux,  O<£-%  which  will 
pass  through  the  meter  disc.  It  can  be  readily  seen  by 
reference  to  the  figure  that  if  the  current,  OI'  is  of  the 
proper  value,  that  this  resultant  flux  Ofa  will  be 
exactly  90  degrees  behind  the  impressed  e.m.f.,  OE. 
By  adjusting  the  amount  of  non-inductive  resistance  in 
the  circuit  of  the  lagging  coil,  this  condition  can  be 
very  easily  produced,  which  process  is  known  as  "lag- 
ging." A  properly  lagged  meter  will  register  with 
accuracy  on  low  power  factor.  The  method  of  lagging 
above  described  is  used  in  meters  manufactured  by  the 
General  Electric  Company. 

The  method  of  lagging  which  is  employed  in 
meters  manufactured  by  the  Westinghouse  Electric 
and  Manufacturing  Company  is  somewhat  different 
from  that  which  has  just  been  explained,  though  the 
principle  is  essentially  the  same.  In  the  Westinghouse 
meter  the  lagging  coil  consists  of  an  adjustable  short- 
circuited  turn,  placed  on  the  pole  tip  of  the  potential 
coil.  The  position  of  this  turn  can  be  adjusted  so  as  to 
obtain  the  required  flux  component  to  bring  the 
resultant  flux  90  degrees  behind  the  impressed  e.m.f. 
By  referring  to  Fig.  18  it  will  be  seen  how  this  is 
accomplished.  OE  represents  the  impressed  e.m.f.,  OI, 
the  current  in  the  potential  coil,  OE',  the  voltage 
induced  in  the  short-circuited  lagging  turn,  OF,  the 
corresponding  current,  and  O<j>'  the  flux  set  up  by  this 
current.  Ofa  represents  the  resultant  flux  which  lags 
90  degrees  behind  the  line  e.m.f.  The  proper  value  of 
the  flux,  O(f>'  can  be  obtained  by  varying  the  position 
of  the  short-circuited  turn. 

In  the  induction  meter  manufactured  by  the  Fort 


THE    INDUCTION    METER 


31 


Fits.  18. 


\  V 


Fiu.  19. 


32 


THE    WATTHOUR    METER 


Wayne  Electric  Works,  the  lagging  device  consists  of 
two  elements,  one  being  wound  on  the  light  load 
adjusting  arm  (shown  at  G,  Fig.  19),  and  is  connected 
in  series  with  the  lagging  resistance,  H.  This  coil  and 
resistance  is  shunted  across  a  portion  of  the  potential 
winding  as  shown.  The  other  coil,  E,  is  wound  on  the 
potential  pole  tip  and  is  short-circuited  through  a 
resistance,  L.  In  the  vector  diagram,  Fig.  20,  OE  is  the 
impressed  e.m.f.,  OI,  the  current  flowing  in  the  poten- 
tial circuit,  which  lags  not  quite  90  degrees  behind  the 
voltage,  and  O<£  is  the  flux  produced  by  this  current. 


Fig,  20. 

This  flux  produces  the  voltage  OEa  in  the  lagging  coil, 
E,  which  in  turn  sets  up  the  current  Ok,  and  the  flux, 
O$2.  The  current  induced  in  the  meter  disc  by  the 
potential  coil  also  sets  up  a  flux,  O<£d,  in  phase  with 
itself.  The  resultant  of  Ofa  and  O<£d,  which  is  repre- 
sented by  O<£R-i,  combines  with  O<£  giving  the  result- 
ant flux  O<£R-2,  which  lags  more  than  the  required  90 
degrees,  and  this  is  brought  to  exactly  90  degrees  by 
the  flux  O03  set  up  by  the  coil,  G.  The  flux  Ocfc,  being 
almost  in  phase  with  OE,  the  voltage  impressed  on  the 


THE   INDUCTION    METER 


33 


coil  being  in  phase  with  OE,  and  the  circuit  being 
closed  through  a  non-inductive  resistance.  The  proper 
amount  of  lagging  is  accomplished  by  adjusting  the 
resistances  H  and  L,  which  changes  the  values  of  the 
currents  Ok  and  OIs,  and  therefore  the  fluxes  produced 
by  them.  Coil  L  is  left  open-circuited  when  used  on 
133  cycles,  the  flux  from  the  meter  disc  producing  the 
necessary  lagging  effect  in  conjunction  with  the  coil, 
H.  Such  a  meter  as  just  described  is  "double  lagged," 
since  the  60  cycle  meter  can  be  used  on  133  cycles  by 
simply  open-circuiting  coil  L. 

Light  Load  Adjustment. 

The  light  load  adjustments  of  the  various  makes 
of  induction  meters  on  the  American  market  are  very 


</ 


Fig.  21. 


similar  in  principle  of  operation,  as  is  also  the  case 
with  the  power  factor  adjustments.  The  different 
manufacturers,  however,  use  somewhat  different 
methods  of  applying  the  fundamental  principle  .as  will 
be  seen  in  the  following  descriptions: 

The  light  load  adjustment  clip  of  the  General 
Electric  induction  meter  is  shown  at  A  in  Fig.  21,  and 
consists  of  a  rectangular  copper  conductor  which  acts 
as  a  short-circuited  loop,  being  so  mounted  that  it  can 
be  shifted  in  a  plane  at  right  angles  to  the  axis  of  the 
potential  pole.  This  short-circuited  turn  has  an  e.m.f. 


34  THE   WATTHOUR   METER 

induced  in  it,  by  the  flux  from  the  potential  pole  tip, 
which  in  turn  sets  up  a  current  that  is  practically  in 
phase  with  this  e.m.f. ;  the  current  produces  a  magnetic 
field  which  is  out  of  phase  with  the  flux  from  the  poten- 
tial pole.  This  flux  from  the  light  load  adjusting  coil 
reacts  with  the  main  flux  from  the  potential  pole  tip 
and  thus  produces  a  turning  effort  which  acts  upon  the 
meter  disc.  The  amount  of  this  turning  effort  can  be 
varied  by  simply  shifting  the  short-circuited  turn,  so 


Fig.  22a. 

that  there  will  be  a  mechanical  as  well  as  a  time  phase 
displacement  between  the  flux  from  it  and  that  pro- 
duced by  the  potential  pole.  The  illustrations  in  Fig. 
22  (a  and  b)  shows  clearly  the  construction  of  the  Gen- 
eral Electric  Company's  single  phase  induction  meter 
for  ordinary  house  use,  from  which  a  general  idea  may 
be  had  of  the  parts  entering  into  the  construction  of  a 
typical  induction  watthour  meter. 


THE    INDUCTION    METER 


35 


36 


THE   WATTHOUR   METER 


The  light  load  adjusting  device  of  the  Fort  Wayne 
induction  meter  consists  of  a  laminated  iron  arm  which 


Fig.  23. 


forms  part  of  the  potential  pole,  and  upon  which  is 
mounted  the  short-circuited  coils.  The  position  of  this 
arm  can  be  shifted,  the  effect  being  similar  to  that 

£>/\sc. 


Fig.  24. 


described  for  the  General  Electric  meter.    Figure  23  is 
an  illustration  of  the  Fort  Wayne  company's  single 


THE    INDUCTION    METER 


37 


phase  meter,  and,  as  will  be  noted,  the  disc  has  a 
peculiar  "cup-shaped"  form.  The  illustration  at  (b) 
shows  the  ease  with  which  the  disc  may  be  removed 
without  disturbing  other  parts  of  the  meter. 

The  light  load  adjusting  device  of  the  Westing- 
house  induction  meter  consists  of  two  adjustable  short- 
circuited  turns  so  mounted  that  they  may  be  rotated 


Fiy.  25a. 

r 

through  a  small  angle.  One  side  of  each  of  these  short- 
circuited  turns  is  in  an  air-gap  in  the  magnetic  circuit 
of  the  potential  winding  and  by  partially  rotating  the 
turn  it  can  be  made  to  enclose  more  or  less  lines  of 
magnetism,  as  can  be  readily  seen  from  the  diagram  in 
Fig.  24  at  A.  The  lines  of  magnetism,  in  passing 
through  the  short-circuited  turns,  induce  currents 
therein,  which  currents  set  up  an  auxiliary  field.  This 


38 


THE   WATTHOUR   METER 


auxiliary  field  is  out  of  phase  with  the  main  field  from 
the  potential  pole,  and  the  two,  acting  in  conjunction, 
produce  a  torque  on  the  meter  disc,  the  amount  of 
which  can  be  varied  by  moving  the  short-circuited 
turns  so  that  they  will  embrace  more  or  less  of  the  flux 
passing  through  the  air-gap.  In  Fig.  25  (a  and  b)  are 
shown  two  views  of  the  single  phase  type  of  induction 
meter  as  manufactured  by  the  Westinghouse  company. 
The  object  of  the  light  load  adjusting  device  is  to 


Fisr.  25b 

produce  a  torque  from  the  potential  circuit  alone  (inde- 
pendent of  the  load  on  the  meter),  the  magnitude  of 
which  will  be  just  enough  to  overcome  the  friction 
of  the  meter,  therefore  rendering  it  accurate  on  light 
loads. 

Creeping. 

If  the  light  load  adjustment  is  set  so  as  to  exert  a 
torque  greater  than  is  actually  necessary  to^overcome 
the'  friction  it  will  cause  "creeping"  on  no  load. 


THE   INDUCTION    METER  39 

Creeping  will  also  result  if  the  light  load  adjustment 
is  properly  set  for  operation  at  normal  voltage  and 
then  the  meter  installed  on  a  circuit  where  the  voltage 
is  considerably  above  the  normal  voltage  rating  of  the 
meter.  A  higher  voltage  will  produce  a  higher  flux 
from  the  potential  pole,  which  in  turn  will  induce  a 
higher  current  in  the  light  load  adjusting  coil,  and  this 
higher  current  and  higher  flux  will  mutually  react  and 
produce  a  higher  no  load  torque,  thereby  causing  the 
meter  to  creep. 

Effect  of  Frequency  Variations. 

When  an  induction  meter  is  operated  on  a  fre- 
quency other  than  that  for  which  it  is  adjusted,  the 
lagging  coil  will  no  longer  set  up  just  the  necessary 
flux  to  bring  the  resultant  flux  from  the  potential  pole 
exactly  90  degrees  behind  the  impressed  e.m.f. ;  it  will 
either  be  ahead  or  behind  this  correct  90  degree  posi- 
tion, depending  upon  whether  the  frequency  is  below 
or  above  the  normal  value.  Errors  from  this  source 
will  be  inappreciable  so  long  as  the  frequency  is  within 
10%  (approximately)  of  the  normal  value. 

It  is  at  the  present  time  the  practice  of  the  leading 
meter  manufacturers  to  design  their  125  cycle  and 
their  133  cycle  meters  so  that  by  a  simple  connection 
or  adjustment,  which  can  be  easily  made,  they  may  be 
used  with  accuracy  on  60  cycle  circuits.  This  is  on 
account  of  the  fact  that  60  cycles  is  the  standard  light- 
ing and  power  frequency,  and  as  the  majority  of  the 
higher  frequency  plants  will  sooner  or  later  be  changed 
over  to  60  cycles,  it  will  evidently  be  a  great  saving 
to  them  if  they  can  use  their  old  meters  rather  than 
have  to  purchase  new  60  cycle  meters  when  such  a 
change  may  be  made.  Meters  so  constructed  are 
known  as  "double  lagged"  meters,  since  they  are 
lagged  at  the  factory  for  two  different  frequencies. 

The  effect  of  a  frequency  other  than  normal  can  be 
best  shown  by  reference  to  the  diagram  shown  in  Fig. 
26,  in  which 


40 


THE   WATTHOUR   METER 


OE=the  impressed  e.m.f., 

OI=current  in  potential  coil  at  normal  frequency, 
OIi=current  in  potential  coil  at  low  frequency, 
Ol2=current  in  potential  coil  at  high  frequency, 

OIL,  OIL-i  and  OIL-2  =  the  currents  in  the  lagging 
coil  for  these  different  frequencies. 


Fig.  26. 


Now  suppose  that  the  meter  is  properly  lagged 
for  a  frequency,  f,  the  current  in  the  potential  winding 
being  OI,  and  the  flux  therefrom  being  O<£.  The  cur- 
rent in  the  lagging  coil  will  be  OIL,  and  the  flux  there- 


THE    INDUCTION    METER  41 

from  will  be  O<£L;  these  two  fluxes,  O<f>  andO<£L  com- 
bine to  produce  the  resultant  flux  Oc/>R,  which  is  exactly 
90  degrees  behind  the  impressed  e.m.f.  Now  suppose 
that  the  meter  is  used  on  a  frequency,  fi,  which  is  below 
normal.  With  a  lower  frequency  the  flux  set  up  by  the 
potential  coil  will  be  greater,  as  the  rate  of  change  of 
flux  must  remain  the  same.  The  magnetizing  current, 
OL,  will  therefore  be  greater,  the  core  loss  and  the  RP 
losses  will  be  higher,  so  that  there  will  be  a  larger 
energy  component  of  the  current,  and  it  will  therefore 
not  lag  by  as  great  an  angle  as  with  normal  frequency ; 
the  current  OL  sets  up  the  flux  O</n,  which  represents 
the  condition  for  a  frequency  below  normal.  The  flux, 
O<£i,  combining  with  the  flux  O<£L-i,  set  up  by  the  lag- 
ging coil  at  the  lower  frequency,  produces  the  resultant 
flux  O<£R-i,  which  does  not  lag  to  the  90  degree  posi- 
tion, and  in  order  that  it  be  made  to  lag  to  the  correct 
90  degree  position,  it  is  necessary  for  the  lag  coil  to 
set  up  a  greater  flux  than  O<£L-i,  which  can  be  accom- 
plished by  relagging  the  meter  for  this  lower  fre- 
quency, fi. 

Now  in  the  case  of  a  higher  frequency,  fa,  the  cur- 
rent in  the  potential  winding  is  represented  by  OL, 
and  the  corresponding  flux  by  Ofa.  Both  the  core  loss 
and  the  RP  losses  in  the  potential  winding  will  now  be 
less  than  in  the  initial  case,  the  energy  component  will 
therefore  be  less,  and  the  flux  will  lag  more  nearly  to 
the  correct  90  degree  position.  The  flux,  O<£L3,  now 
set  up  by  the  lagging  coil,  will  combine  with  the  flux 
O$2,  producing  the  resultant  flux  O</>R-z,  which  lags  too 
much,  being  beyond  the  90  degree  position.  In  order 
for  the  resultant  flux  to  lag  to  the  correct  position,  it 
will  therefore  be  necessary  for  the  lagging  coil  to  set 
up  a  flux  less  than  O<£L-2;  in  other  words,  the  meter 
would  have  to  be  relagged  for  this  higher  fre- 
quency, fa. 

Obviously,  for  power  factors  other  than  unity, 
serious  errors  would  be  introduced  by  using  a  meter 
adjusted  for  a  frequency  different  from  that  of  the 
circuit  on  which  it  operates ;  the  meter  might  either 


42  THE   WATTHOUR    METER 

run  fast' or  slow,  depending  upon  whether  it  is  adjusted 
for  a  higher  or  lower  frequency  than  that  of  the  cir- 
cuit on  which  it  operates,  and  upon  whether  the  cur- 
rent is  lagging  or  leading. 

The  effect  of  a  frequency  above  normal  will  be  to 
make  the  meter  run  fast  on  lagging  currents  and  slow 
on  leading  currents ;  a  frequency  below  normal  will 
cause  the  meter  to  run  slow  on  lagging  currents  and 
fast  on  leading  currents.  For  unity  power  factor  there 
would  also  be  an  error  introduced,  although  it  would  not 
be  so  pronounced  as  in  the  case  of  power  factors  other 
than  unity.  In  this  case  only  that  component  of  the 
flux  from  the  potential  pole  which  is  in  the  correct  90 
degree  position  will  be  effective,  so  that  the  phase  dis- 


placement  of  the  resultant  flux  will  tend  to  make  the 
meter  run  slow-  on  any  frequency  other  than  that  for 
which  the  meter  is  adjusted.  The  values  of  the  result- 
ant fluxes  are  not  strictly  proportional  to  the  fre- 
quencies, however,  since  the  component  supplied  by  the 
lagging  coil  is  not  proportional  to  the  frequency  and 
its  angular  relation  to  the  main  component  is  different 
for  the  different  frequencies ;  also  for  lower  frequencies, 
the  energy  component  of  the  voltage  is  greater  and  the 
reactive  component  is  less,  due  to  the  increased  shunt 
current  which  tends  to  make  the  meter  run  slow,  and 
vice  versa  for  higher  frequencies. 

The  currents  induced  in  the  meter  disc  by  the  cur- 
rent coils  should  be  directly  proportional  to  the  fre- 
quency, but  due  to  the  demagnetizing  effect  of  these 


THE    INDUCTION    METER 


43 


currents  on  the  current  coil  poles,  this  condition  is  not 
strictly  fulfilled,  which  causes  the  meter  to  have  a 
tendency  to  run  slow  on  frequencies  above  normal  and 
fast  on  frequencies  below  normal. 

The  resultant  effect  of  the  different  disturbing 
factors  above  mentioned  will  affect  the  meter  to  an 
extent  dependent  largely  upon  the  design. 

Figure  27  is  a  curve  showing  the  accuracy  of  a 


Fig.  28. 

standard  make  of  induction  meter  on  different  fre- 
quencies at  unity  power  factor,  and  Fig.  28  shows  the 
load  and  voltage  curves  of  a  standard  5  ampere  induc- 
tion meter  operating  at  normal  frequency. 


Connections  of  Single  Phase  Meters. 


SOL// 


Fig.  29. 


Fig.  29  shows  the  diagram  of  connections  for  a 


44 


THE   WATTHOUR   METER 


single  phase  watt-hour  meter  when  used  on  a  single 
phase  two  wire  circuit. 

Fig.  30  shows  the  connections  of  two  single  phase 
meters  connected  so  as  to  register  the  power  flowing 
in  a  single  phase  three  wire  circuit,  and  Fig.  31  shows 
one  three  wire  single  phase  meter  connected  for  the 
same  conditions.  The  three  wire  meter  in  effect  is 


Fig.  30. 

really  two  meters  with  but  one  disc  and  one  potential 
coil,  but  with  a  current  coil  in  each  side  of  the  line. 


Source 


Fig.  31. 

The  fact  that  the  three  wire  meter  has  but  one  poten- 
tial winding  will  cause  an  error  in  its  registration  if 
the  voltage  between  each  line  and  the  neutral  is  not 
the  same.  The  polyphase  meter  can  also  be  used  as 
a  single  phase  three  wire  meter,  and  is  not  subject 


THE   INDUCTION    METER 


45 


to  the  error  just  mentioned,  but  owing  to  its  greater 
cost,  it  is  seldom  used  for  this  purpose. 

One  single  phase  two  wire  meter  can  also  be  used 
to  register  the  power  flowing  in  a  single  phase  three 
wire  system  by  using  it  in  connection  with  a  special 
"three  wire"  current  transformer.  Such  a  transformer 
has  two  primary  windings  and  one  secondary  winding. 
The  two  primary  windings  are  connected  respectively 
in  series  with  each  side  of  the  line,  the  current  in  the 
secondary  being  proportional  to  the  vector  sum  of  the 


Fig.  32. 


currents  in  the  two  primaries.  The  connections  of  a 
single  phase  meter  when  used  with  such  a  transformer 
are  shown  in  Fig.  32. 

Single  Phase  Meters  on  Polyphase  Circuits. 

Two  single  phase  meters  may  be  used  to  register 
the  power  being  supplied  by  either  a  two  phase  or  a 
three  phase  system.  For  a  two  phase  four  wire  sys- 
tem, one  meter  should  be  connected  in  each  phase  as 


46 


THE   WATTHOUR    METER 


shown  in  Fig.  33,  and  when  so  connected,  each  meter 
will  register  the  power  in  its  respective  phase ;  the 
algebraic  sum  of  the  readings  of  the  two  meters  will 
then  be  the  total  power  supplied  by  the  two  phase 
system. 


4-   Source 


Fig.  33. 


In   the   case   of  a   three   phase   system,    the   two 
single  phase  meters  should  be  connected  as  shown  in 


•3  Source. 


Fit.  34. 


Fig.  34.  (Similar  connections  for  potential  and  cur- 
rent transformers  are  shown  in  the  appendix,  Figs. 
33a,  34a.)  The  action  of  the  two  meters  thus  connected 
can  best  be  explained  by  reference  to  the  vector  dia- 
gram, Fig.  35,  in  which  AC,  CB  and  AB  represent  the 


THE    INDUCTION    METER 


47 


voltages  between  the  phases  2  and  i,  i  and  3,  and  3 
and  2  respectively ;  also  let  CO,  BO  and  AO  represent 
the  currents  in  the  phases  i,  3  and  2  respectively,  for 
the  condition  of  unity  power  factor,  and  C'O,  B'O  and 
A'O  the  currents  for  a  power  factor  other  than  unity. 


t 


Fig.  35. 


We  will  first  consider  the  case  of  a  balanced  sys- 
tem.   In  this  case  let  e  represent  the  e.m.f.  between  a 

£ 

line  and  neutral,  then  e  =  i/^T»  when  E  is  the  voltage 

between  lines;  also  let  I  represent  the  current  per 
phase  in  a  balanced  system.  A  three  phase  system 
may  be  considered  as  consisting  of  three  single  phase 
systems  with  the  neutral  as  a  common  return;  the 
voltages  of  each  of  the  single  phase  systems  being 


48  THE   WATTHOUR    METER 

represented  by  e,  and  the  current  by  I.  The  power  in 
each  single  phase  system  will  be  =  (e  I)  cos  0,  where 
0  is  the  angle  by  which  the  current  is  displaced  in 
phase  from  the  voltage,  (Fig.  35)  ;  the  power  in  the 
three  phase  system  will  therefore  be  the  sum  of  the 
power  in  the  three  equivalent  single  phase  systems, 
or,  numerically, 

ip 

P  =  3  e  I  cos  0;  and  since  e  =     . — , 

we  have  P  =  \/3  E  I  cos  0,  which  is  the  funda- 
mental equation  for  the  power  flowing  in  a  three 
phase  system. 

The  two  meters  connected  as  shown  in  Fig.  34 
will  each  have  a  current  I  flowing  through  it,  and  a 
voltage  E  impressed  upon  its  potential  winding.  In 
meter  No.  I,  the  current  is  represented  by  the  line 
CO  (Fig.  35),  and  the  voltage  by  CA;  and  in  meter 
No.  2  the  current  is  represented  by  B'O,  and  the  volt- 
age by  AB ;  the  current  being  represented  as  being 
out  of  phase  by  the  angle  0.  The  angle  OCA  =  angle 
OBA  =  30  degrees,  which  is  the  angular  displacement 
between  the  impressed  voltage  and  the  line  current  for 
unity  power  factor.  For  power  factors  other  than 
unity,  this  angular  displacement  is  equal  to  30  degrees 
plus  or  minus  the  angle  9,  and  as  can  be  readily  seen 
from  the  diagram  it  will  be  (30°  —  6)  for  one  meter  and 
(30°  +  6)  for  the  other  meter. 

The  power  p',  registered  by  one  meter  will  there- 
fore be 

p' =  E  I  cos  (30° +  0),  and  the  power  p",  regis- 
tered by  the  other  meter  will  be  p"  =  E I  cos 
(30°  —  6),  from  which 

p'  +  p"  =  El  cos  (30°  +  0)  +  El  cos  (30°  —  0) 
=  El   [cos  (30°  +  0)  +  cos   (30°  —  6}  ] 
=  El  [2  cos  (30°  cos  0)  ]  and  since  cos  30°= 

I/2\/3, 

we  have 
p'  +  P"  =  El  V3  cos  0,  which,  as  shown  above,  is  the 


THE   INDUCTION    METER  49 

equation  for  the  power  flowing  in  a  three  phase  sys- 
tem. It  is  therefore  seen  that  two  single  phase  meters 
will  register  correctly  the  power  in  a  balanced  three 
phase  system. 

An  unbalanced  three  phase  system  may  be  con- 
sidered as  consisting  of  a  balanced  system  with  the 
addition  of  an  unbalancing  component  of  either  cur- 
rent, voltage  or  both.  When  using  two  single 
phase  meters  on  an  unbalanced  three  phase  system, 
the  unbalanced  component  will  be  taken  care  of  as 
follows : 

Suppose  that  in  addition  to  the  balanced  current, 
there  is  a  current  flowing  between  the  phases  2  and  3 
(Fig.  35),  or  between  2  and  i ;  this  current  would  flow 
either  through  meter  No.  i  or  meter  No.  2,  and  as  the 
meter  through  which  it  would  flow  has  impressed 
upon  it  the  voltage  of  the  phases  between  which  this 
current  is  flowing,  the  meter  would  register  the  power 
correctly.  In  the  case  of  an  unbalanced  current  pass- 
ing between  phases  3  and  i,  such  current  would  flow 
through  both  meters,  and  if  this  unbalanced  current 
is  in  phase  with  the  voltage  BC,  between  phases  3  and 
i,  it  will  be  60°  out  of  phase  with  the  voltage  im- 
pressed upon  each  meter,  and  as  the  cosine  of  60°  is 
1/2,  the  correct  amount  of  power  will  be  registered, 
one-half  being  registered  by  each  meter.  If  this  cur- 
rent is  not  in  phase  with  BC,  it  will  be  out  of  phase 
more  than  60°  in  one  meter,  and  less  than  60°  in  the 
other  meter ;  the  correct  amount  of  power  will  still 
be  registered,  but  it  will  not  still  be  equally  divided 
between  the  two  meters.  The  angle  by  which  this 
unbalanced  current  will  be  out  of  phase  in  one  meter 
will  be  (60°  +  6),  and  in  the  other  it  will  be  (60°  —  0), 
where  0  is  the  angle  of  displacement  between  the  un- 
balanced current  and  the  voltage  BC.  The  power 
registered  by  one  meter  will  be  =  E  i  cos  (60°  +  0), 
where  i  =  the  unbalanced  current,  and  that  registered 
by  the  other  would  be  =  E  i  cos  (60°  —  0),  and  the 
total  unbalanced  power  would  be, 


50 


THE   WATTHOUR   METER 


p  —  E  i  cos  (60°  +  0)  +  E  i  cos  (60°  -  -  0), 
=  E  i  (2  cos  60° cos  0),and  since  cos  6o°=i/2, 

we  have  p  =  E  i  cos  6,  which  shows  that  the  power 
would  be  correctly  registered  in  the  case  of  an  unbal- 
anced current. 

Unbalanced  voltages  would  be  taken  care  of  in  a 
similar  manner.  An  unbalanced  voltage  across  phases 
i  and  2,  or  across  2  and  3,  would  directly  affect  the 
potential  winding  of  one  or  the  other  of  the  single 
phase  meters.  An  unbalancing  of  the  voltage  across 
phases  3  and  i  would  affect  both  meters  by  distorting 
the  voltage  triangle  so  that  the  power  transmitted 
would  still  be  correctly  registered. 


Fig.  36. 

Another  method  of  connecting  two  single  phase 
meters  to  register  the  power  in  a  three  phase  system 
in  conjunction  with  current  and  potential  trans- 
formers is  shown  in  Fig.  36;  the  relations  of  the  cur- 
rents and  voltages  being  shown  in  the  vector  diagram, 
Fig.  37.  Let  I,  I'  and  I"  represent  the  currents  in  the 
three  legs  of  a  three  phase  system ;  E  being  the  volt- 
age between  lines  and  e  the  voltage  between  any  line 
and  neutral.  Also  let  0,  0',  and  6"  represent  the  angles 
by  which  the  currents  are  displaced  from  the  position 
of  unity  power  factor;  we  will  assume  the  voltage  to 


THE   INDUCTION    METER 


51 


be  balanced,  since  this  makes  the  explanation  some- 
what simpler.  The  true  power  is  P  =  e  I  cos  0  +  e  I' 
cos  0'  -f-  e  I"  cos  0".  Meter  No.  I  has  currents  I  and  I' 
flowing  through  its  winding  (that  is,  the  resultant  of 
these  currents),  and  the  voltage,  E,  CA,  impressed 
upon  it ;  it  is  used  with  a  multiplier  of  1/2. 

Meter  No.  2  has  the  current  I"  flowing  through  it, 
and  the  voltage  Bn,  impressed  upon  it ;  Bn  =  (3/2)  e. 
Let  P  represent  the  total  power,  P'  the  power  regis- 
tered by  meter  No.  i  and  P"  the  power  registered  by 
meter  No.  2, 


Fig.  37. 

P'  =  El'  cos  (30°  —  0')  +  El  cos  (30°  +  0). 


cos 


0 


P  =  y+  P' 

El'  cos  (30—  0')+  El  cos  (30  +  0)  ,    3     T,,        „„ 
^—  *~2~       C° 

and  cos  (30°  —0')  =  cos  30°  cos  0'  +  sin  30°  sin  0' 
cos  (30°  +  0)  =  cos  30°  cos  0  —  sin  30°  sin  0; 


52  THE   WATTHOUR    METER 


-  y-  * 

also,  cos  30°  =  ^—?-,  sin  30°  =  ^  and  e  =  ^7= 

2  1/3 


whence?-  -^-  cos  0  -      ^-+±-^-cos 

r 


2  2 

=  V  3   E  (I   cos  0  +  I'  cos  0'  )  +  ~~  (I'  sin  0' 


cos 


0"r. 


The  vector  sum  of  the  currents  in  a  three  phase 
three  wire  system  is  zero,  therefore  I"  cos  6"  =  I  cos 
(60  —  0)  +  T  cos  (60  +  0'),  reducing  this  we  get 

I'sin  Q'  —  I  sin  0=    — p=[  l/2  (I  cos  0  +  J'  cos  0')  —  I" 

r  i) 

cos  ^",]  substituting  this  for  I'  sin  0  -  -  I    sin   0   in   the 
above  and  substituting  K    3  e  for  E,  we  derive, 

P=:^-e  (I  COS0  +  I'  cos  0')  +  -| -    (ycos0 

+       -«•  /!/  T"  /I"  \         I  «^  C      T //  /V/ 

—  cos  0  -  -  I    cos  0  )  -+-  —  I    cos  V  . 

whence  P  =  e  I  cos  0  +  e  I'  cos  0'  -f-  e  I"  cos  0". 

The  particular  feature  of  this  connection  is  that  it 
gives  an  indication  of  how  well  the  system  is 
balanced;  if  the  system  is  perfectly  balanced  the  two 
meters  will  register  the  same  power,  taking  into  con- 
sideration, of  course,  the  multiplier  of  1/2.  This  is 
true  with  the  connection  previously  described  and 
most  often  used,  only  when  the  power  factor  is  unity. 
If  the  system  is  perfectly  balanced,  either  of  the 
meters  can  be  relied  upon  to  record  the  total  power, 


THE    INDUCTION    METER 


53 


regardless  of  the  value  of  the  power  factor,  in  which 
case  the  dials  of  meter  No.  I  would  be  read  without 
a  multiplier,  and  meter  No.  2  would  have  a  dial  multi- 
plier of  2. 


Fig.  38. 


In  Fig.  38  is  shown  the  connections  of  three,  single 
phase  meters  for  measuring  the  power  in  three  phase, 
three  and  four  wire  systems.  The  three  phase  circuit 
is  metered  in  this  case  simply  as  three  single  phase 
circuits,  the  current  in  each  phase  being  the  current 
in  one  of  the  single  phase  circuits,  and  the  voltage  of 
each  single  phase  circuit  being  the  voltage  from  the 
corresponding  line  to  the  neutral.  The  sum  of  the 
readings  of  the  three  meters  will  be  the  kilowatt- 
hours  supplied  by  the  three  phase  system. 

The  advantage  of  this  connection  for  the  three 
wire  system  is  that  the  meters  operate  under  better 
power  factor  conditions  than  with  the  usual  two  meter 
method.  With  this  method  the  current  and  e.m.f.  of 
each  meter  will  be  in  phase  when  the  power  factor  of 
the  load  being  metered  is  unity,  while  with  the  two 


54 


THE   WATTHOUR    METER 


meter  method  the  current  and  e.m.f.  are  30°  out  of 
phase. 

Figure  38  (a)  shows  another  method  of  connect- 
ing the  potential  transformers  for  measuring  the 
power  flowing  in  a  three  phase  three  wire  system  by 
means  of  three  single  phase  meters.  This  connection, 
with  certain  primary  voltages,  permits  the  use  of 
standard  ratio  potential  transformers,  where  the 
connection  shown  in  Fig.  38  will  require  ratios 
other  than  the  standard.  This  method  is  especially 
applicable  to  2300  volt  circuits,  the  standard  potential 


Fig.  38a. 


transformer  used  in  this  case  would  be  rated  2200 
volts  primary,  and  110/122  volts  secondary,  the  higher 
secondary  voltage  (122)  being  used  as  is  indicated  in 
the  figure.  With  a  2300  volt  primary,  a  secondary 
voltage  of  approximately  220  volts  would  be  obtained 
from  the  potential  transformers,  thereby  permitting 
the  use  of  standard  220  volt  meters.  When  meters  are 

R  X  R' 
used  in  this  manner,  a  multiplying  factor, z ,     is 


THE    INDUCTION    METER 


55 


employed  in  obtaining  the  total  reading,  in  which  R  = 
the  ratio  of  the  current  transformers  and  R'  =  ratio 


of  the  potential  transformers  (= 


2200. 

122  ' 


Determination  of  Power  Factor  by   Means   of  Two 

Single  Phase  Meters. 

The  method  of  metering  with  two  single  phase 
meters  on  a  balanced  three  phase  system  has  an  ad- 
vantage over  the  polyphase  meter  when  it  is  desired 


Fig.  38b. 


to  obtain  the  average  power  factor  of  the  load,  which 
can  be  done  by  applying  the  following  formula: 

Average  Power  Factor  = 


2  I/CP')2—  (P'  X  P")  +  (P")2 

where  P'  and  P"  represent  the  readings  of  the  two 
single  phase  meters.  The  deduction  of  this  formula  is 
as  follows:  In  the  vector  diagram,  Fig.  38  (b)  AB, 
AC  and  BC  represent  the  voltages  between  the  phases 


56  THE   WATTHOUR   METER 

of  a  three  phase  circuit,  and  OI,  OI'  and  OI"  repre- 
sent the  currents  in  the  legs  I,  2  and  3  respectively, 
and  which  are  displaced  from  the  position  of  unity 
power  factor  by  the  angle  6.  Now  suppose  that  the 
current  coil  of  meter  No.  i  is  connected  in  leg  No. 
2,  and  that  its  potential  coil  is  connected  across  AB  ; 
also  that  the  current  coil  of  'meter  No.  2  is  connected 
in  leg  No.  3  and  its  potential  coil  across  AC.  Then 
the  power,  P',  being  registered  by  meter  No.  i  will 
be  =  AB.  OF  cos  <£,  where  <£  is  the  angle  between  AB 
and  OF  =  (30°  +  0),  0  'being  the  angle  of  current  dis- 
placement. The  angle  OBA  is  of  course  30°.  Denot- 
ing the  voltage  AB  by  E,  and  the  current  OI'  by  I, 
we  have  P'  =  El  cos  (30  +  6)  and  similarly,  the  power 
being  registered  by  meter  No.  2  will  be  P"  =  El  cos 
(30  —  6),  (assuming  the  system  to  be  balanced). 
Then  by  trigonometry  we  have, 

cos  (30  +  6)  =  cos  30  cos  0  —  sin  30  sin  0 
cos  (30  —  0)  =  cos  30  cos  6  -f-  sin  30  sin  0 
But  cos  30°  =  1/2  V3^  and  sin  30°  =  1/2, 

Therefore  cos  (30  +  0)  =  1/2  y~$cosO  —  1/2  sin  0 
and  cos  (30  —  9)  =  1/2  V^  cos  0  +  1/2  sin  0 

Substituting  these  values  in  the  above  equations  for  P' 
and  P"  we  have  : 

P'  =  El  (l/2  >XTcos  0  —  1/2  sin  0),  hence 


FI  _=  _         __ 

(  1/2  V  3  cos  0  —  1/2  sin  0) 

P"  =  El  (  !/2  T/Tcos  0  +  1/2  sin  0),  hence 

P" 

El  =  -  7=  —      -  or   since    El  =  El, 
(1/2  V  3  cos  0  +  l/2  sin  0) 

we  have 

P'  P" 


l/2  V  3  cos  0  —  l/2  sin  0       l/2  V  3  cos  0  +  V2  sin  0 


THE   INDUCTION    METER 


57 


By  trigonometry,  sin  0  ==  V  \  —  cos  20,  and   sub- 
stituting this  value 


cos 


I/TP'  cos  o  +  p'  v  \  —  cos2  e  ==  p"  i/ 

0  -  -   P"    V  1  —  cos2  0,    V  1  —  cos2  0    (?'  +  P") 

-  (P"  —  P')  /T  cos  0. 
Squaring  and  transposing,  we  have, 
cos2  0  [  4  (P')2  —  4  P'  P"  +  4  (P")2  ]  =  (P'  +  P")2, 
Whence 


P'  +  P' 


^average  power  factor 


The  true  instantaneous  power  factor  can  also  be 
determined  by  this  method,  using  two  indicating  watt- 
meters. 


58 


THE   WATTHOUR   METER 


Single  Phase  Meters  for  Six  Phase  Circuits. 

Three  single  phase  meters  can  be  used  for  meas- 
uring the  power  in  a  six  phase  system  by  connecting 
them  as  shown  in  Fig.  39. 

Polyphase  Meters. 

The  polyphase  induction  watthour  meter  for  use 
on  either  a  two  or  three  phase  system  consists  essen- 
tially of  two  single  phase  meter  elements  mounted 
one  above  the  other  on  the  same  shaft,  and  having 
but  one  register.  The  principle  of  operation  is  iden- 
tically the  same  as  that  previously  explained  for  two 
single  phase  meters,  except  that  in  the  case  of  the 
two  single  phase  meters,  the  algebraic  sum  of  the 
two  registers  is  taken  to  obtain  the  total  power,  while 


So. 


Fig.  40. 

in  the  case  of  the  polyphase  meter  this  is  automatically 
accomplished  by  having  the  two  discs  connected  to 
one  shaft.  The  polyphase  meter  has  the  advantage 
of  being  easy  to  read  and  install. 

The  polyphase  meter  for  use  on  three  phase  four 
wire  systems  when  used  without  current  transformers 
is  of  somewhat  different  construction  from  the  meter 
used  on  three  phase  three  wire,  or  on  two  phase  sys- 
tems. In  the  three  phase  four  wire  meter  without  cur- 
rent transformers,  it  is  necessary  to  have  a  current 
winding  in  the  meter  for  each  phase.  These  wind- 
ings are  arranged  on  the  two  elements  in  such  a  man- 
ner that  the  current  in  one  phase  passes  through  a 


THE   INDUCTION    METER  59 

winding  on  each  element;  the  current  in  each  of  the 
other  two  phases  passing  through  a  winding  on  one 
element.  Fig.  40  shows  the  vector  diagram  and  also 
the  diagram  of  connections  of  this  type  of  meter,  in 
which  I,  I'  and  I"  represent  the  currents  in  phases  i,  2 
and  3  respectively,  and  i-n,  2-n  and  3~n  represent  the 
voltages  between  the  legs  i,  2  and  3  and  the  neutral 
wire,  n.  One  element  of  the  meter  has  the  voltage  3-n 
impressed  upon  its  potential  winding,  and  the  current 
I"  passing  through  one  set  of  current  coils,  and  the 
current  I'  passing  through  the  other  set  of  current 
coils.  The  other  element  has  the  voltage  i-n  im- 
pressed upon  its  potential  winding,  and  the  current,  I 
passing  through  one  set  of  current  coils,  and  the  cur- 
rent I'  passing  through  the  other  set. 

A  three  phase  four  wire  system  is,  in  effect,  three 
single  phase  systems,  the  current  in  each  system  being 
the  current  in  the  corresponding  phase,  and  the  volt- 
age of  each  system  being  the  voltage  between  the 
corresponding  phase  and  the  neutral. 

With  the  connections  described  above,  the  power 
being  transmitted  by  each  of  the  two  single  phase  sys- 
tems, 3-n  and  i-n  will  be  correctly  recorded  by  the 
meter  for  both  unity  power  factor  and  for  power  fac- 
tors other  than  unity,  as  each  element  of  the  meter 
will  act  as  a  single  phase  meter  in  recording  this 
power.  The  power  being  transmitted  by  single  phase, 
2-n  will  be  recorded  partly  by  one  meter  element  and 
partly  by  the  other.  The  current  I'  passes  through 
both  meter  elements,  the  connections  to  its  coils  being 
reversed  so  that  for  unity  power  factor  it  is  60°  out  of 
phase  with  the  voltage  impressed  on  each  element. 
(If  these  coils  are  not  reversed  the  current,  I'  will 
pass  through  the  meter  120°  out  of  phase  with  the 
voltages  impressed  on  the  two  elements  and  will  sub- 
tract instead  of  adding  the  power  in  phase  2-n.) 

Since  the  cosine  of  60°  =  1/2,  one-half  of  the 
power  will  be  recorded  by  each  element.  For  power 
factors  other  than  unity,  one  element  will  record 
more  than  half,  and  the  other  element  will  record  less 


60  THE   WATTHOUR   METER 

than  half  the  power  being  transmitted;  the  sum  of 
the  power  recorded  by  both  elements  will  be  equal 
to  the  total  power. 

When  current  transformers  are  used  with  three 
phase  four  wire  meters,  the  standard  polyphase  meter 
as  used  on  three  phase  three  wire  circuits  may  be 
used,  the  current  transformers  being  so  connected 
that  the  resultant  current  of  phases  3  and  2  passes 
through  the  current  coils  of  one  element,  the  voltage, 
3-n  being  impressed  on  this  element;  the  resultant 
-current  of  phases  I  and  2  passes  through  the  current 


C-r 

\ 

t 

| 

2 

-E 

•i  —  _  r-| 

3  , 

-  CT. 

J 

J_ 

1 

, 

j 

ej 

! 

! 

Fiff.  41. 

coil  of  the  other  element  which  has  the  voltage  i-n 
impressed  upon  it. 

The  action  of  this  type  of  meter  is  the  same  as 
just  described  for  the  meter  without  current  trans- 
formers. In  the  latter  case,  two  sets  of  current  coils 
are  used  on  each  meter  element,  the  resultant  effect 
of  the  currents  in  these  two  sets  of  coils  being  the 
same  as  the  resultant  of  the  currents  from  two  current 
transformers  passing  through  one  set  of  current  coils. 

Fig.  41  shows  the  proper  connections  for  a  poly- 
phase meter  when  used  on  a  three  phase  four  wire 
system  in  conjunction  with  current  transformers. 


THE    INDUCTION    METER  61 

Adjustment  of  Elements. 

Polyphase  meters  should  be  provided  with  some 
means  of  adjusting  the  torque  of  one  of  the  elements 
without  disturbing  the  other.  This  is  necessary  be- 
cause there  is  only  one  retarding  system  which  is 
common  to  both  elements,  and  it  is  therefore  necessary 
that  some  means  be  provided  so  that  the  two  electrical 
elements  may  be  adjusted  to  give  the  same  torque 
when  the  same  amount  of  power  is  passing  through 
each.  This  adjustment  is  readily  accomplished  by 
changing  the  number  of  turns  on  the  potential  wind- 
ing of  one  of  the  elements.  By  this  means,  the  torque 
of  that  particular  element  can  be  adjusted  to  be  the 
same  as  that  of  the  other  element.  This  is  done  in 
some  meters  by  bringing  out  a  number  of  taps  from 
the  potential  winding,  having  a  very  few  number  of 
turns  between  taps,  so  that  a  fine  adjustment  can  be 
accomplished. 

Other  meters  employ  what  is  known  as  a  "bal- 
ance loop,''  which  is  a  short-circuited  turn  whose  posi- 
tion can  be  so  changed  that  it  will  introduce  more 
or  less  reluctance  in  the  path  of  that  portion  of  the 
flux  from  the  potential  winding  which  does  not  pass 
through  the  meter  disc.  Increasing  this  reluctance 
will  cause  more  of  the  flux  to  pass  through  the  meter 
disc,  while  decreasing  it  will  cause  less  flux  to  pass 
through  the  disc.  After  adjusting  the  "balance  loop'r 
the  meter  should  be  "re-lagged." 

The  balance  between  the  elements  of  a  polyphase 
meter  can  also  be  altered  by  changing  the  air  gap  be- 
tween the  potential  and  the  current  coil  poles  of  one 
element ;  this  can  be  accomplished  by  loosening  the 
screws  and  prying  the  poles  further  apart  or  by  using 
a  light  wooden  mallet  to  drive  them  closer  together. 
The  adjustment  obtained  by  this  means  is  necessarily 
very  rough,  but  it  is  sometimes  useful  (usually  when 
putting  a  new  potential  coil  in  place)  to  bring  the 
elements  within  the  range  of  adjustment  provided  by 
the  manufacturer. 


62 


THE   WATTHOUR    METER 


Interference  of  Elements. 


Polyphase  meters  are  subject  to  one  source  of 
error  from  which  two  single  phase  meters  used  on 
polyphase  circuits  are  entirely  free,  that  being  the 
"interference  of  elements,"  which  is  due  to  the  inter- 
ference or  reaction  of  the  magnetic  fields  of  one 
element  with  the  fields  of  the  other,  and  in  some  cases 
it  introduces  errors  amounting  to  as  much  as  4%  or 
5%.  For  this  reason  the  elements  should  not  be  placed 
too  close  together.  In  a  well  designed  meter  operat- 
ing near  unity  power  factor,  the  error  from  this  source 
should  never  amount  to  more  than  0.5%. 


Polyphase  Meters  on  Six  Phase  Circuits. 


Fig.  42. 


Fig.  42  shows  the  proper  connections  of  two  poly- 
phase meters  when  used  to  measure  the  power  flowing 
in  a  six  phase  system. 


THE   INDUCTION    METER 


63 


Metering  High  Potential  Circuits. 
When  meters  are  used  on  high  potential  circuits, 
the  secondaries  of  both  the  potential  and  the  current 
transformers  should  be  solidly  grounded.  This  is  not 
only  a  precaution  for  the  safety  of  those  who  have  to 
read  and  test  the  meter,  but  it  also  prevents  undue 
strain  between  the  windings  of  the  meter.  Both  the 
potential  and  the  current  transformers  act  as  con- 


Ground 


Source          17 


Fig.  43. 

densers,  and  so  do  the  windings  of  the  meter  them- 
selves. The  voltage  of  the  system  is  thus  impressed 
across  several  condensers  in  series,  the  strain  across 
each  condenser  being  inversely  proportional  to  its 
electro-static  capacity.  It  is  possible  for  the  strain 
thus  impressed  to  reach  a  value  which  will  puncture 
the  insulation  from  the  winding  to  the  core. 

Fig.  43  shows  the  connections  for  both  a  single 


64  THE   WATTHOUR    METER 

and  a  polyphase  meter  when  used  with  current  and 
potential  transformers,  showing  the  ground  connec- 
tion to  be  made  when  used  on  high  potential  circuits. 

When  metering  the  high  tension  side  of  a  "Y" 
connected  three  phase  system,  the  current  trans- 
formers can  be  relieved  of  a  great  part  of  the  high 
tension  strain  by  connecting  them  between  the  power 
transformers  and  the  neutral  or  "Y"  point.  This  will 
also  protect  the  current  transformers  from  lightning 
and  high  potential  surges,  as  each  current  transformer 
will  have  a  power  transformer  between  itself  and 
the  line. 

Current  and  potential  transformers  used  with 
watt-hour  meters  should  never  be  operated  under  the 
condition  of  overloads,  and  it  is  best  to  have  them 
operate  considerably  underloaded.  Overloading  the 
transformers  will  cause  the  meters  to  run  slow. 

Current  transformers  are  usually  rated  at  so  many 
watts,  for  instance,  40  watts.  The  sum  of  the  volt- 
amperes  taken  by  all  the  meter  coils  in  series  with 
such  a  transformer  plus  the  volt-amperes  consumed  in 
the  leads  to  the  meters  should  never  exceed  this 
amount  and  should  preferably  be  less. 

Potential  transformers  are  usually  rated  at  from 
10  to  200  watts.  The  total  load  in  volt-amperes  should 
never  exceed  the  rating  and  where  a  high  degree  of 
accuracy  is  required  the  total  load  should  be  con- 
siderably less  than  the  rating. 

In,  making  connections  of  polyphase  watthour 
meters  care  should  be  taken  to  see  that  the  meter  is 
connected  exactly  in  accordance  with  the  diagram  fur- 
nished by  the  manufacturer;  if  this  is  not  done,  the 
meter  may  be  connected  so  that  it  will  run  in  the 
proper  direction,  but  the  interference  between  ele- 
ments will  be  high  ;  this  will  be  the  case  if  both  the 
current  and  potential  connections  of  one  element  are 
reversed. 


CHAPTER  IV. 

THE   COMMUTATING  TYPE   OF  WATTHOUR 
METER. 

During  the  past  few  years  the  commutating  type 
of  watthour  meter  has  practically  been  superseded  by 
the  induction  type  for  use  on  alternating  current  sys- 
tems, and  at  the  present  time  its  use  is  principally  in 
connection  with  direct  current  work. 

The  commutating  meter  (as  well  as  other  types) 
is  in  reality  a  direct  connected  motor-generator,  the 


Fig.  44. 

motor  being  of  the  shunt  type,  having  its  armature 
connected  in  multiple  (or  parallel)  with  the  source  of 
supply  and  with  its  field  coils  in  series  with  the  load 
to  be  measured.  The  revolving  aluminum  (formerly 
copper)  disc  and  the  retarding  magnets  comprise  the 
generator.  As  the  disc  D,  Fig.  44,  revolves  between 
the  jaws  of  the  retarding  magnets  M,  it  cuts  the  lines 
of  magnetic  force,  thus  producing  "Foucault"  or 
"eddy"  currents  in  the  disc.. 


66  THE   WATTHOUR    METER 

Principle  of  Operation. 

The  torque,  or  turning  effort,  of  the  motor  is 
proportional  to  the  product  of  the  magnetic  flux  set  up 
by  the  armature  and  that  set  up  by  the  series  field 
coils.  The  magnetic  flux  of  the  armature  is  propor- 
tional to  the  impressed  e.  m.  f.,  and  the  magnetic  flux 
of  the  series  field  coils  is  directly  proportional  to  the 
current  flowing  through  them.  The  product  of  the 
current  and  the  voltage  equals  the  power,  therefore 
the  turning  effort  of  the  armature  is  directly  propor- 
tional to  the  power  being  expended  in  the  circuit  C. 
The  power  generated  and  expended  in  the  disc  itself 
depends  directly  upon  the  speed,  since  the  eddy  cur- 
rents generated  depend  upon  the  rate  at  which  the 
magnetic  lines  are  cut,  therefore  the  drag  on  the  disc 
will  be  directly  proportional  to  the  speed.  We  there- 
fore have  an  instrument  in  which  the  turning  effort  is 
proportional  to  the  power  passing  through  it,  and  in 
which  the  retardation,  neglecting  friction,  is  propor- 
tional to  the  speed.  Since  the  speed  will  increase  until 
the  torque  just  balances  the  retardation,  the  revolving 
element  will  turn  at  a  speed  proportional  to  the  power 
passing,  which  is  the  condition  sought.  The  revolu- 
tions of  the  armature  are  transmitted  through  a  suit- 
able train  of  gears  to  the  dials  which  register  in  units 
of  electrical  work,  such  as  the  watthour  or  the  kilo- 
watthour. 

Comparison  to  a  Shunt  Motor. 

There  is  one  essential  difference  between  the 
ordinary  shunt  motor  and  the  motor  of  a  commutating 
watthour  meter,  ana  that  is  the  fact  that  the  latter  has 
no  iron  or  steel  in  its  magnetic  circuit.  If  iron  were 
employed  in  the  meter,  its  torque  would  no  longer  be 
strictly  proportional  to  the  current  flowing  in  the 
series  field  coils,  due  to  the  "saturation"  effect  of  the 
iron,  which  would  result  in  a  greater  reluctance  (or 
magnetic  resistance),  with  an  increase  in  current. 
Therefore,  on  light  loads,  the  torque  would  be  corre- 
spondingly greater  than  at  full  load,  thereby  causing 
the  meter  to  over-register  on  light  loads,  provided,  of 


COMMUTATING    TYPE.  67 

course,  that  it  was  adjusted  to  register  correctly  on 
full  load,  or  vice  versa. 

It  is  a  well  known  fact  that  the  ordinary  shunt 
motor  will  increase  in  speed  if  the  field  current  is 
decreased,  because  the  armature  will  then  have  to  run 
faster  in  order  to  generate  the  "back"  or  counter 
e.  m.  f.,  under  the  conditions  of  a  weaker  field.  On  the 
other  hand,  a  watthour  meter  will  decrease  in  speed 
with  a  decrease  in  field  current,  or  vice  versa.  These 
two  facts  are  apparently  contradictory  and  may  be 
accounted  for  as  follows :  The  speed  of  a  shunt  motor 
is  proportional  to  the  impressed  e.  m.  f.,  and  inversely 
to  the  field  strength,  and  must  be  such  that  the  back 
e.  m.  f.  is  equal  (plus  the  RI  drop)  to  the  impressed 
e.  m.  f.  Any  weakening  of  the  field  will  therefore 
cause  an  increase  in  speed,  since  the  armature  con- 
ductors have  to  cut  the  decreased  field  at  a  higher  rate 
in  order  to  generate  the  same  back  e.  m.  f.  (For  a  full 
explanation  of  this  theory,  see  any  text  book  on  direct 
current  motors.)  In  the  case  of  the  meter,  however, 
the  counter  e.  m.  f.  is  inappreciable,  the  impressed 
e.  m.  f.  being  practically  all  absorbed  in  the  resistance 
of  the  armature,  the  auxiliary  or  "compensating  field," 
and  in  the  external  resistance  if  any  is  used.  So  long 
as  the  voltage  remains  unchanged,  the  armature  cur- 
rent will  therefore  remain  unchanged,  irrespective  of 
the  changes  in  the  series  field  strength  and  the  speed. 
The  effect  of  a  decrease  in  field  strength  is  to  decrease 
the  torque,  with  a  consequent  decrease  in  speed  until 
the  retarding  torque  exerted  by  the  permanent  mag- 
nets on  the  disc  is  decreased  to  correspond  to  the 
turning  effort  of  the  armature.  With  an  increase  in 
field  strength  the  reverse  takes  place,  that  is,  the  re- 
action between  the  armature  current  and  the  stronger 
field  produces  a  stronger  turning  effort  which  increases 
the  speed  until  the  retarding  effect  of  the  permanent 
magnets  increases  to  a  corresponding  degree.  This 
condition  of  the  operation  of  the  meter  holds  true  for 
an  ordinary  shunt  motor  until  the  counter  e.  m.  f.  is 
more  than  about  50  per  cent  of  the  line  potential, 


68  THE   WATTHOUR    METER 

below  which  point  the  speed  of  the  shunt  motor  would 
increase  with  the  field  strength,  and  above  which  point 
the  speed  would  decrease  when  the  field  strength  was 
increased.  Thus  it  will  be  seen  that,  in  reality,  there 
is  no  discrepancy  between  the  motor  of  a  meter  and 
the  ordinary  shunt  motor. 

Efficiency. 

The  efficiency  of  a  meter  is  based  upon  the  actual 
watts  lost  in  the  resistance  of  the  series  field  coils  and 
the  potential  circuit  (which  includes  the  armature,  the 
compensating  field  and  the  external  resistance),  the 
losses  due  to  friction,  and  the  losses  in  the  disc  due  to 
eddy  currents  set  up  by  the  retarding  magnets. 

During  the  early  development  of  the  watthour 
meter  of  the  commutator  type,  the  loss  in  the  poten- 
tial circuit  alone,  in  a  100  voltmeter  was  about  10 
watts,  and  in  the  200  voltmeters  was  about  20  watts ; 
such  meters  are  now  termed  "low  efficiency"  meters ; 
the  present  type  or  "high  efficiency"  meter  has  a  loss 
in  the  potential  circuit  of  about  4  or  5  watts  in  the 
100  volt  meter,  and  a  loss  in  the  series  field  coils  not 
exceeding  i  per  cent  of  the  total  capacity  of  the  meter 
in  the  smaller  capacity  meters  and  much  less  than  this 
in  the  large  capacity  meters.  The  reduction  in  losses  has 
been  accomplished  by  increasing  the  resistance  in  the 
potential  circuit  and  by  almost  doubling  the  number 
of  conductors  on  the  armature ;  the  number  of  arma- 
ture conductors  being  increased  to  produce  a  greater 
torque. 

General  Construction. 

Fig.  45  illustrates  interior  views  of  three  repre- 
sentative types  of  commutating  meters,  in  which  (a)  is 
the  Westinghouse,  (b)  the  General  Electric,  and  (c) 
the  Duncan,  all  of  American  manufacture. 

The  meter  shown  at  (c)  is  designed  for  use  on 
direct  current  circuits,  although  it  may  be  said  that 
the  Duncan  alternating  current  meter  is  very  similar 
in  construction,  and  ks  operation  essentially  the  same 


COMMUTATING   TYPE. 


69 


70  THE   WATTHOUR    METER 

as  the  direct  current  meter.  The  use  of  the  commu- 
tating  type  of  meter  on  alternating  current  circuits 
will  be  dealt  with  later  in  this  chapter. 

The  Compensating  or  Shunt  Field. 

The  function  of  the  compensating  or  shunt  field  is 
to  compensate  for  friction,  especially  at  light  loads. 
When  a  meter  is  operating  on  a  very  small  percentage 
of  its  rated  load,  the  ratio  of  friction  to  torque  is 
relatively  great,  therefore  the  lighter  the  load  the 
greater  will  be  the  retarding  effect  of  friction.  In 
order  to  overcome  this  friction  effect,  the  compensat- 
ing field  is  connected  in  series  with  the  armature  so 
that  its  flux  will  work  in  conjunction  with  the  main  or 
series  field.  In  the  General  Electric  and  Westing- 
house  meters,  the  strength  of  the  compensating  field 
is  constant,  and  the  "helping  out"  or  compensating 
effect  is  altered  by  moving  it  closer  to  or  further  from 
the  armature,  so  that  more  or  less  of  its  flux  embraces 
the  armature.  In  the  Duncan  meter,  the  amount  of 
compensation  is  altered  by  means  of  the  multi-point 
switch  shown  in  the  illustration.  This  switch  is  con- 
nected to  various  taps  on  the  compensating  winding 
and  the  variation  is  accomplished  by  cutting  in  or  out 
a  certain  number  of  the  coils,  thereby  altering  the 
flux. 

When  the  compensating  field  was  first  used,  it 
was  permanently  fastened  to  the  inside  of  the  series 
field  coils.  This  method  was  soon  superseded  by 
mounting  it  on  an  adjustable  rack,  so  that  it  could  be 
moved  toward  or  away  from  the  armature  and  then 
clamped  in  the  correct  position.  The  compensating 
field  should  be  so  designed -that  (in  a  new  meter)  it 
will  allow  a  maximum  boosting  effect  of  about  10  per 
cent  on  light  load,  that  is,  it  should  have  sufficient 
strength  when  adjusted  for  full  compensation,  to  in- 
crease the  speed  of  the  meter  by  about  10  per  cent 
when  the  meter  is  operating  on  5  per  cent  of  full  load. 
This  allows  sufficient  margin  for  adjustment  as  the 
friction  increases.  Writh  compensating  fields  designed 
to  give  a  greater  boosting  effect,  the  meter-man  is  apt 


COMMUTATING    TYPE.  71 

to  take  advantage  of  the  quick  method  of  temporarily 
adjusting  the  meter  and  thereby  compensate  for  ex- 
cessive friction  which  by  all  means  should  be  located 
and  removed. 

In  the  older  types  of  meters  (with  especial  refer- 
ence to  the  Thompson  recording  type),  on  account  of 
the  low  armature  resistance,  it  was  necessary  to  place 
an  external  resistance  in  series  with  the  compensating 
field,  such  resistance  being  mounted  in  card  form  on 
the  back  of  the  meter  case.  This  method  has  been 
simplified  by  having  the  entire  resistance  of  the  poten- 
tial circuit  (external  to  the  armature)  self-contained 
in  the  compensating  field  in  all  meters  up  to  and 
including  250  volts.  For  the  500  and  6oo-volt  types,  it 
is  still  the  practice  to  furnish  a  suitable  external 
resistance  for  the  potential  circuit. 

Brushes. 

It  is  very  important  that  the  brushes  be  made  of 
a  material  which  will  not  vary  in  elasticity,  and  when 
once  properly  adjusted  they  should  maintain  their 
tension  permanently.  The  control  of  the  brush  ten- 
sion is  effected  either  by  gravity  or  by  a  spring.  The 
actual  contact  surface  of  the  brush  should  be  made  of 
silver  since  it  has  been  found  from  practice  that  this 
material  gives  better  service  under  operating  con- 
ditions. Each  brush  (i.  e.,  each  positive  and  each 
negative)  is  usually  divided  into  two  parts,  so  as  to 
give  a  more  even  distribution  of  pressure  at  the  point 
of  contact,  and  to  make  the  brush  self-aligning.  Brush 
friction  has  been  considerably  reduced  by  using  a 
cylindrical  rather  than  a  flat  type, 

The  Commutator. 

During  recent  developments  in  the  manufacture  of 
meters,  the  diameter  of  the  commutator  has  been 
materially  reduced,  and  at  the  present  time  some 
makes  employ  a  diameter  of  less  than  one-tenth  of  an 
inch  in  meters  of  no  and  220  volts  capacity.  This 
reduction  in  the  size  of  the  commutator  has  greatly 
reduced  the  friction  of  that  particular  member.  It  is 


72  THE   WATTHOUR    METER 

general  practice  to  make  the  commutator  bars  of  pure 
silver,  since  this  metal  suffers  least  from  oxidization, 
and  therefore  it  presents  a  smoother  surface  and  more 
constant  contact  resistance,  two  features  which  are 
desirable.  The  commutator  is  usually  built  up  directly 
on  the  shaft,  the  bars  being  insulated  from  it  and  from 
each  other  and  are  held  intact  by  a  metal  ferrule  on 
each  end  of  the  commutator,  the  ferrules,  of  course, 
being  properly  insulated  from  the  bars.  In  some  cases 
the  commutator  bars  are  insulated  from  each  other  by 
fibre  bars  or  other  solid  insulating  material,  and  in 
other  cases  simply  by  an  air  space.  Each  of  these 
methods,  under  certain  conditions,  are  liable  to  give 
trouble.  When  a  hard  insulating  material  is  used,  it 
is  apt  to  wear  down  slower  than  the  commutator  bars, 
causing  the  brushes  to  "ride,"  and  thereby  opening 
the  armature  circuit,  which  will  either  cause  the  meter 
to  stop  or  else  cause  severe  sparking.  In  case  a  soft 
material  is  used  it  is  apt  to  gum  the  commutator  and 
give  rise  to  the  same  trouble  as  too  hard  an  insulation. 
The  trouble  due  to  air-insulated  bars,  is  that  under 
extreme  conditions,  the  air  space  may  become  filled 
with  dust  and  small  particles  of  metal,  thereby  causing 
adjacent  bars  to  become  short-circuited.  A  meter 
should  be  inspected  often  enough,  though,  so  that 
under  average  commercial  conditions  the  commutator 
with  air-space  insulation  will  give  good  service  and 
will  very  probably  be  superior  to  the  commutator  with 
solid  insulation. 

The  Armature. 

There  are  two  general  types  of  armature  con- 
struction at  the  present,  the  spherical  and  the  rect- 
angular. The  tendency  is  to  favor  the  spherical  type, 
since  this  construction  permits  the  field  coils  to  be  so 
designed  as  to  allow  a  minimum  leakage  of  magnetic 
flux,  thus  securing  the  highest  possible  torque  for  a 
given  watt  loss  in  the  fields  and  armature  windings, 
and  thus  approximating  more  nearly  the  condition  of 
an  ideal  meter. 

In  both  the  spherical  and  the  rectangular  wound 


COMMUTATING   TYPE.  73 

armatures,  the  winding  is  of  the  well-known  ''Siemens 
drum  type."  The  rectangular  winding  is  usually  sup- 
ported by  two  spiders  made  of  small  strips  of  hard 
wood  and  properly  secured  in  position  on  the  shaft. 
The  supporting  medium  in  the  spherical  wound  arma- 
ture consists  of  two  hemispherical  pieces  of  fibre 
which  are  mounted  directly  on  the  shaft,  the  windings 
themselves  being  held  in  position  by  grooves  which 
are  stamped  in  the  fibre  shells.  This  construction  is 
good  mechanically  and  insures  a  very  light  weight  of 
moving  element.  The  full  load  speed  of  the  commu- 
tating  type  of  meter  is  usually  about  40  r.  p.  m.,  which 
further  permits  of  very  light  armature  construction. 

Generally  speaking  the  armatures  of  meters  for 
use  on  no-volt  circuits  or  thereabouts  usually  have  8 
armature  coils  of  about  1000  turns  each,  of  number 
.003  copper  wire,  and  those  of  200  volts  and  above 
have  16  coils  of  500  turns  each,  of  the  same  size  wire. 
This  method  of  subdividing  the  coils  on  the  higher 
voltages  is  followed  so  that  there  will  not  be  such  a 
great  difference  of  potential  between  adjacent  coils 
nor  between  the  commutator  bars.  There  is  one  com- 
mutator segment  per  coil,  for  instance,  in  a  loo-volt 
meter  there  will  be  8  commutator  segments,  and  in  a 
2OO-volt  meter  there  will  be  16  segments. 

The  total  armature  resistance  in  meters  from  100 
volts  to  600  volts  inclusive,  of  the  ordinary  house  type, 
is  usually  between  1000  and  1200  ohms,  the  proper 
amount  of  resistance  being  placed  in  series  to  limit 
the  current  on  the  various  voltages.  The  armature 
current  is  practically  the  same  for  all  voltages  from 
100  to  600  inclusive,  the  total  resistance  of  the  poten- 
tial circuit  being  subdivided  approximately  as  shown 
in  the  table  below: 


DO  CO  O  ••-       „  ^        en 

fag  Sg  g  g    -2«  s^2 

TYPE  OF   METER               ~|  ||  -|  Sg||  ||| 

2  D  Cu  "o  i)  "o  o'o.i:  i-  3  S 


5  amp.,  2  wire,  110  v 1,300          1,200          2,500          5          0.0447 

5  amp.,   2  wire,   220  v 3,800          1,200          5,000        10          0.0447 

5  amp.,  2  wire,  550  v 10,900          1,200        12,100        25          0.0454 


74 


THE    WATTHOUR    METER 


It  is  thus  seen  that  the  armature  current  is  prac- 
tically constant. 

While  on  the  subject  of  armatures,  it  should  be 
borne  in  mind  that  the  temperature  coefficient  of  the 
armature  and  the  disc  should  be  the  same,  so  that  any 


decrease  in  torque  of  the  armature,  due  to  a  rise  in 
temperature,  will  be  correspondingly  offset  by  a  rise 
in  resistance  of  the  disc,  which  in  turn  would  decrease 
the  effect  of  the  retarding  magnets. 

Other   features   of   construction   have   been   dealt 
with  in  Chapter  I. 


COMMUTATING    TYPE.  75 

The   Use  of  the  Commutating   Meter  on  Alternating 
Current  Circuits. 

As  previously  explained,  the  commutating  type 
meter  is  a  simple  shunt  motor,  and  this  being  the 
case,  the  question  may  arise,  "Why  is  it  that  such  a 
meter  can  be  operated  with  accuracy  on  alternating 
current  circuits?"  It  should  first  be  remembered  that, 
owing  to  the  iron  in  the  magnetic  circuit  of  an  or- 
dinary shunt  motor,  there  would  be  a  great  difference 
in  phase  relation  between  the  current  in  the  armature 
and  the  current  in  the  fields  if  such  a  machine  was 
supplied  with  alternating  current,  this  being  due  to 
the  much  greater  inductance  of  the  field  winding.  The 
current  in  the  fields  would  lag  almost  90  degrees  be- 
hind the  current  in  the  armature,  therefore  the  torque 
produced  would  not  be  sufficient  to  cause  rotation. 
The  meter,  being  as  it  is,  devoid  of  iron  in  its  mag- 
netic circuit,  will  not  suffer  from  such  a  phase  differ- 
ence when  supplied  with  alternating  current. 

The  commutating  type  of  meter  can  be  made  to 
operate  with  accuracy  on  alternating  current  circuits 
by  making  an  adjustment  which  is  termed  "lagging." 
If  this  type  of  meter  is  used  on  alternating  current, 
precisely  the  same  as  on  direct  current — that  is,  with- 
out any  adjustments — the  current  in  the  armature  will 
lag  a  few  degrees  behind  the  impressed  voltage,  while 
the  current  in  the  field  coils,  for  a  load  of  unity  power 
factor,  will  be  in  phase  with  the  impressed  voltage; 
the  lag  in  the  armature  current  being  caused  by  the 
inductance  of  the  armature  and  the  compensating  field. 
This,  however,  does  not  introduce  a  serious  error  at 
unity  power  factor.  In  order  that  the  meter  may  regis- 
ter correctly  on  power  factors  other  than  unity,  it  is 
necessary  that  the  current  in  the  armature  be  in  phase 
with  the  current  in  the  series  field  when  the  meter  is 
operating  on  a  load  of  unity  power  factor.  It  is  there- 
fore necessary  that  an  adjustment  be  made  that  will 
bring  the  two  currents  in  phase,  thereby  correcting 
the  small  phase  difference  above  referred  to.  Such  an 
adjustment  is  accomplished  by  shunting  a  part  of  the 


76  THE    WATTHOUR    METER 

•current  in  the  series  fields  through  a  non-inductive 
resistance.  By  properly  adjusting  this  resistance,  the 
current  in  the  series  fields  can  be  made  to  "lag"  until 
it  is  in  phase  with  the  armature  current. 

The  principle  or  theory  of  this  method  of  ad- 
justment may  be  explained  as  follows:  The  series 
coils  have  both  resistance  and  inductance,  and  when 
shunted  by  a  non-inductive  resistance,  the  line  current 
is  divided  into  two  components,  one  of  which  flows 
in  the  non-inductive  resistance  and  the  other  in  the 
field  coils  themselves.  (The  current  in  the  non-induc- 
tive resistance  is  a  small  percentage  of  that  flowing 
in  the  field  coils.)  The  relative  values  of  these  two 
components  of  the  line  current  are  inversely  propor- 
tional to  the  impedances  of  the  two  paths,  and  the 
phase  angle  between  them  will  depend  upon  the  ratio 
of  the  resistance  to  the  reactance  of  the  series  coils. 
This  is  diagramatically  shown  at  (a)  in  Fig.  47,  where 
OV  represents  the  impedance  drop  around  the  series 
-coils  and  the  non-inductive  resistance  together ;  i  being 
the  current  in  the  resitance  and  i'  the  current  in  the 
series  field  coils.  The  voltage  drop,  Ri,  in  the  non- 
inductive  resistance,  will  be  =OV,  and  i  will  be  in 
phase  with  OV.  The  drop  in  the  series  coils,  however, 
consist  of  two  components,  a  resistance  drop,  R',  i', 
which  is  in  phase  with  i',  and  a  reactive  drop  xi'  at  90 
degrees  from  i',  the  phase  angle  between  i  and  i'  being 
represented  in  the  figure  by  $. 

The  main  line  current  is  made  up  of  these  two 
components  as  shown  at  (b)  in  Fig.  47,  and  it  can  be 
seen  from  this  that  the  angle  p,  which  is  the  lag  of  the 
current  i'  in  the  series  coils  behind  the  line  current  I, 
can  be  adjusted  by  merely  changing  the  value  of  the 
current  i  in  the  non-inductive  resistance. 

After  having  properly  lagged  the  meter  on  say 
50%  power  factor,  it  is  necessary  to  recalibrate  it, 
since  the  torque  exerted  by  the  series  coils  will  be 
less  than  before  the  adjustment  was  made,  as  the 
total  line  current  is  no  longer  flowing  in  the  series 
•coils.  This  recalibration  is  made  by  adjusting  the  re- 


COMMUTATING    TYPE. 


77 


tarding  magnets,  after  which  the  meter  will  be  ac- 
curate for  all  power  factors  above  50%.  An  unlagged 
commutator  meter  will  have  a  tendency  to  run  fast 
on  inductive  loads.  In  any  event,  where  it  is  neces- 
sary to  lag  commutating  meters  it  is  advisable  to  take 
the  subject  up  with  the  manufacturer  of  the  meter  in 
question,  and  obtain  their  recommendations.  In  all 

V 


xz' 


Tt'i' 


Fig.  47. 

cases  involving  a  great  number  of  meters,  it  is  advis- 
able to  change  the  entire  installation  over  to  the  in- 
duction type  on  account  of  its  greater  simplicity  and 
superior  operation  on  alternating  currents. 

Three-Wire  Meters. 

In  the  heart  of  cities,  and  in  buildings  where  a 
large  amount  of  current  is  used,  the  three-wire  system 
of  distribution  is  almost  always  to  be  recommended 
on  account  of  the  great  saving  in  the  amount  of  copper 
in  the  distributing  wires,  the  most  common  system 
being  the  220/1  lo-volt  system,  the  current  being  fur- 
nished (in  case  of  direct  current)  by  either  a  three- 


78 


THE   WATTHOUR    METER 


wire  generator,  a  two-wire  generator  with  a  balancer 
set,  or  by  two  generators  operating  on  a  three-wire 
connection.  The  question  often  arises  as  to  what 
extent  should  the  distributing  company  insist  upon 
having  the  system  balanced.  In  New  York  City  the 


•O'cx/rce 


Fig.  48. 

requirements  are  very  rigid.  For  instance,  all  light- 
ing circuits  taking  more  than  five  amperes  must  be 
equally  divided  between  the  two  sides  of  the  system, 
and  all  motors  over  5  h.p.  must  be  connected  across 
the  outside  wires.  On  the  other  hand,  some  com- 


Fie.  49. 

panics  pay  no  attention  whatever  to  the  "balance,"  and 
depend  upon  the  average  conditions  to  balance  the 
load  at  the  station  bus-bars.  At  the  point  of  distribu- 
tion, however,  the  conditions  may  not  be  so  favorable 
as  at  the  station,  thereby  resulting  in  poor  service  on 


COMMUTATING    TYPE 


7'.' 


one  side  or  the  other  of  the  system.  It  is  therefore 
recommended  that  some  effort  be  made  to  keep  the 
load  fairly  well  divided  between  each  of  the  two  out- 
side wires  and  the  neutral. 

To  measure  the  power  flowing-  in  a  three-wire 
system,  it  is  necessary  to  use  two  meters  connected 
as  shown  in  Fig.  48,  or  to  use  one  three-wire  meter 
whose  internal  connections  are  shown  diagramatically 
in  Fig.  49.  The  only  way  in  which  the  three-wire 


7=" 


Fig.  50. 

meter  differs  from  the  ordinary  two-wire  meter  is  that 
in  the  former  the  series  field  coils  are  divided  into 
two  equal  sections,  which  are  connected  in  the  oppo- 
site sides  of  the  system  as  shown  above. 

There  are  devices  on  the  market  for  automatically 
connecting  the  potential  circuit  to  the  opposite  side  of 
the  line  without  reversing  the  direction  of  rotation 
of  the  meter  in  case  one  side  of  the  three  supply  wires 
should  be  disconnected. 


80  THE   WATTHOUR    METER 

The  armature  circuit  is  usually  connected  be- 
tween the  neutral  and  one  of  the  outside  wires  in  the 
three-wire  meters,  because  such  practice  permits 
cheaper  construction,  due  to  the  lower  voltage  im- 
pressed. (In  Fig.  50,  P  represents  the  armature  cir- 
cuit and  FF  the  series  field  coils.)  In  either  case- 
that  is,  with  the  armature  circuit  across  the  outside 
wires  or  across  one  outside  wire  and  the  neutral — the 
three-wire  meter  is  subject  to  error  on  unbalanced 
loads ;  if  connected  to  neutral  it  may  register  either 
slow  or  fast,  depending  upon  whether  the  voltage  be- 
tween C  and  B  (Fig.  50)  is  less  than  or  greater  than 
one-half  the  voltage  between  A  and  B.  If  the  poten- 
tial circuit  is  tapped  from  A  and  B,  the  meter  will 
usually  register  high  on  unbalanced  voltage,  as  the 
lower  voltage  will  usually  be  on  the  heavier  loaded 
side.  It  is  very  seldom  that  the  unbalancing  of  the 
road  on  a  three-wire  system  is  such  that  it  will  cause 
any  great  degree  of  inaccuracy,  but  if  extreme  ac- 
curacy is  a  question  of  prime  importance  it  is  recom- 
mended that  two  two-wire  meters  be  used  rather  than 
one  three-wire  meter  on  a  poorly  balanced  system. 

High   Capacity  Meters   for   Switchboard   Service. 

In  order  that  the  distributing  company  may  have 
an  exact  comparison  between  the  power  actually  de- 
livered from  the  station  bus-bars  and  the  delivered 
power  from  which  a  revenue  is  realized,  it  is  of  the 
utmost  importance  that  switchboard  meters  be  care- 
fully selected  as  to  their  accuracy  and  their  capacity. 
The  question  of  "over-metering"  as  brought  out  in 
Chapter  I  applies  with  even  more  force  in  the  case 
of  switchboard  meters — the  detection  of  unwarrant- 
able losses  depends  primarily  upon  the  switchboard 
meters.  It  will  be  found  iti  almost  every  case  that  it  is 
more  desirable,  for  several  reasons,  to  use  individual 
meters  on  the  various  generators  or  feeders  than  to 
use  "total-output"  meters.  In  the  first  place,  if  a 
single  meter  is  used,  its  capacity  will  have  to  be 
greatly  in  excess  of  the  average  load,  in  order  that  it 
may  take  care  of  the  "peak"  load,  consequently  the 


COMMUTATING    TYPE 


XI 


large  meter  will  be  running  far  below  its  maximum 
efficiency  the  greater  part  of  the  time.  Secondly,  if  it 
is  desired  at  any  time  to  increase  the  capacity  of  the 
station,  the  individual  method  of  metering  will  be 
found  to  be  much  more  flexible  than  will  the  total 
output  meter  method.  In  the  third  place,  it  is  much 
more  convenient  to  test  the  smaller,  individual  meters, 
on  account  of  their  lighter  connections  and  the  ease 


Fig.  51. 

with  which  testing  instruments  may  be  inserted  in  the 
circuits.  All  switchboard  meters  should  be  so  in- 
stalled that  future  testing  may  be  done  with  the  least 
possible  trouble  and  inconvenience. 

High  capacity  meters  for  direct  current  switch- 
board service  are,  in  almost  every  case,  subjected  to 
the  influence  of  powerful  stray  fields  produced  by  the 
bus-bars  which  are  usually  in  close  proximity  to  the 
meters ;  short-circuits  and  overloads  also  give  rise  to 


82  THE    WATTHOUR    METER 

disturbing  influences.  In  order  that  switchboard 
meters  be  free  from  such  disturbances,  special  con- 
struction is  necessary.  Fig.  51  is  an  example  of  a 
high  capacity  meter,  the  one  illustrated  being  for  3000 
amperes.  The  two  armatures  are  "astatically"  ar- 
ranged— that  is,  they  are  so  connected  that  should  the 
influence  of  a  stray  field  tend  to  weaken  the  torque  of 
one  armature,  it  will  correspondingly  strengthen  the 
other,  and  vice  versa.  It  will  also  be  noticed  that  the 
retarding  magnets  are  completely  shielded  by  a  rec- 
tangular metal  box  which  is  built  up  of  soft  steel 
punchings,  which  will  effectually  divert  any  stray 
lines  of  magnetic  force  which  would  otherwise  affect 
the  accuracy  of  the  meter.  Very  often  it  is  found 
necessary  to  place  such  a  shield  on  a  meter  after  it 
has  been  installed,  after  which  it  will  also  be  necessary 
to  recalibrate  the  meter,  because  the  close  proximity 
of  the  shield  to  the  retarding  magnets  will  cause  a 
leakage  of  flux,  thereby  decreasing  the  retardation  of 
the  magnets.  This  effect  is  usually  slight,  but  it  is  al- 
ways better  to  recalibrate  the  meter. 

The  series  field  coils  of  the  meter  shown  in  Fig. 
51  are  of  the  "bus-bar"  type,  the  magnetic  field  being 
produced  by  a  straight  copper  bar  which  carries  the 
current  from  one  of  the  large  studs  past  the  armature 
to  the  other  stud,  the  effect  being  that  of  a  single  turn. 
The  standard  sizes  of  this  type  range  from  2000  to 
10,000  amperes  at  potentials  from  100  to  600  volts 
inclusive. 

Switchboard  watthour  meters  ranging  in  current 
from  50  to  1500  amperes  have  the  same  astatic  features 
as  above  noted,  but  instead  of  having  the  "bus-bar" 
field  coil,  they  have  several  turns  of  heavy  copper. 
Their  damping  system  should  also  be  encased  in  a 
protecting  steel  box  when  the  meter  is  in  the  neigh- 
borhood of  conductors  carrying  large  currents. 

Another  difference  between  the  switchboard  type 
of  meter  and  the  ordinary  house  type  is  that  in  the 
former,  all  resistance  in  series  with  the  armature  or 
the  compensating  field  is  usually  external  to  the 


COM  MUTATING    TYPE 


83 


meter  case,  thus  minimizing  the  heating  effect  from 
this  source. 

In  selecting  a  switchboard  meter,  the  following 
points  should  be  borne  in  mind :  The  meter  should  have 
a  high  torque,  continued  high  accuracy,  light  weight 
of  moving  element,  and  should  have  its  armatures  and 
retarding  magnets  astatically  arranged. 

A  recent  development  has  been  made  in  the  de- 
sign of  switchboard  meters  which  further  protects  it 
against  the  disturbing  influence  of  stray  fields.  This 
is  accomplished  by  making  the  "motor"  a  four-pole 
rather  than  a  two-pole  motor.  By  this  arrangement  it 
is  possible  to  place  two  adjacent  (positive  and  nega- 
tive) poles  much  closer  together  than  in  the  case  of 
the  two-pole  design.  It  will  therefore  be  readily  seen 
that  a  stray  field  coming  from  any  direction  will  tend 
to  more  equally  strengthen  one  pole  and  correspond- 
ingly weaken  the  other,  than  in  the  case  of  a  two-pole 
meter. 

This  type  of  meter  can  of  course  be  used  for  or- 
dinary service  as  well  as  for  switchboard  service,  pro- 
vided the  conditions  warrant  the  expense  of  the  four- 
pole  meter. 

Connections  of  Commutating  Type  Meters. 

The  connections  of  the  commutating  type  of  watt- 
liour  meters  when  used  on  direct  current  circuits  are 
so  simple  that  it  is  not  deemed  necessary  to  give  but 
a  few  characteristic  connections  which  are  shown  in 
the  following  figures : 


Fig.  52. 


84 


THE    WATTHOUR    METER 


Fig.  52  shows  the  connections  of  a  small  capacity 
(3  to  50  amps.)  two-wire  "T.  R.  W."  meter,  of  which 
there  are  still  quite  a  number  in  service.  Fig.  53  is  the 
same  type  meter  for  two-wire  service  in  capacities  of 
from  75  to  1200  amperes.  Fig  54  is  the  "T.  R.  W." 
three-wire,  3^  to  150  ampere  meter. 


From 


73 
Lo&ct 


Fig.  54. 


Fig.  55  shows  the  connections  of  the  General  Elec- 
tric type  "C"  watthour  meter  for 

5  to  25  amperes,  500/600  volts,  2  wire  (C-6  and  C-7) 
50  amperes,  100/250  volts,  2  wire  (C-6). 


COM  MUTATING   TYPE  85 

Fig  56  is  the   connection    of    a   General   Electric 


75  to  600  amperes,  100/250  volts,  2  wire  (C-6  and  C-y). 
50  to  600  amperes,  250/600  volts,  2  wire  (C~7). 

It  will  be  noticed  that  in  Fig.  56  that  only  one 
line  wire  is  carried  through  the  meter  on  account  of 
the  large  size  of  the  conductors. 


Fig,  55. 


Fig.  56. 


Fig.  57. 


Fig.  58. 


Fig.    57    shows    connections    of   a   General    Electric 
type  "C": 

5  to  50  amperes,  200/240  volts,  3-wire  meter. 
Fig.    58    shows    connections   of   a   General    Electric 
type  "C": 

75  to  300  amperes,  200/240  volts,  3-wire  meter. 


86 


THE   WATTHOUR    METER 


La  &  & 


Fie.  60. 

59  and  60  show  connections  of  the  Westing- 
house  two-wire  and  three-wire  direct-current  meters, 
respectively. 


CHAPTER  V. 


THE  MERCURY 


FLOTATION 
METER. 


WATTHOUR 


The   Sangamo   Electric   Company   of   Springfield, 
111.,  manufactures  a  type  of  watthour  meter  which  is 


Fig.  61a.     Sangamo  Meter. 


radically  different  in  operation  from  the  induction  and 
commtitating  types  of  meters  previously  explained. 
The  Sangamo  meter  is  of  the  mercury  flotation  type 
and  its  principle  of  operation  is  based  on  an  old  dis- 
covery made  by  the  scientist,  Faraday,  when  he  found 


88 


THE    WATTHOUR    METER 


that  a  pivoted  metalliq  disc  carrying  electric  current 
would  tend  to  rotate  when  under  the  influence  of  a 
magnetic  field. 

The  fundamental  discovery  of  Faraday  is  very 
ingeniously  utilized  in  the  Sangamo  meter.  A  copper 
disc  is  enclosed  in  a  suitable  chamber  made  of  moulded 
insulating  material  which  is  divided  horizontally  into 


Fig.  61  b.     SanRamo  Meter.  Cover  Removed. 

two  sections,  the  chamber  being  partially  filled  with 
mercury.  In  the  lower  part  of  the  mercury  chamber 
there  are  imbedded  two  copper  terminals  which  serve 
to  conduct  the  current  to  the  copper  disc  through  the 
intervening  mercury.  The  mercury  serves  the  double 
purpose  of  conducting  the  current  to  the  disc  and  of 
buoying  up  the  disc  so  as  to  make  the  weight  on  the 
lower  bearing  very  slight.  The  copper  terminals  are 


MERCURY    FLOTATION  89 

arranged  diametrically  opposite  as  will  be  seen  from 
Fig.  62.  The  exciting  magnet  which  produces  the  flux 
which  acts  upon  the  disc  is  imbedded  in  one  section  of 
the  moulded  "mercury  chamber." 


In  the  case  of  the  direct  current  Sangamo  meter 
the  main  line  current,  or  a  proportional  part  thereof, 
passes  through  the  copper  disc,  the  magnet  being 
excited  from  the  potential  of  the  circuit  upon  which 
the  meter  is  being  used.  In  the  case  of  the  alternating 
current  meter,  the  method  of  excitation  is  opposite 


90  THE    WATTHOUR    METER 

from  the  direct  current  meter,  that  is,  the  magnet  is 
excited  by  the  line  current,  and  the  disc  carries  a 
current  which  is  proportional  to  the  potential  of  the 
circuit. 

The  reaction  of  the  current  in  the  disc  with  the 
magnetic  lines  of  force  from  the  magnet  will  cause  the 
disc  to  rotate  at  a  speed  which  will  be  proportional  to 
the  product  of  the  current  and  the  impressed  e.m.f.,  in 
other  words,  it  will  rotate  at  a  speed  which  will  be 
proportional  to  the  power  being  expended  in  the  circuit 
to  which  it  is  connected.  In  alternating  current  meters 
operating  on  a  circuit  whose  power  factor  is  other  than 
unity,  the  speed  of  rotation  will  then  be  proportional  to 
the  current,  the  e.m.f.,  and  the  power  lacior. 

Under  ordinary  conditions  a  variation  in  tempera- 
ture between  10°  F.,  below  zero,  and  no0  F.,  will  not 
materially  affect  the  operation  of  the  mercurjf  meter, 
but  temperatures  above  or  below  these  maximum  and 
minim-urn  values  are  liable  to  affect  the  accuracy. 
There  is  sufficient  space  in  the  mercury  chamber  and 
such  a  (comparatively)  small  percentage  variation  in 
the  volume  of  the  mercury  with  changes  in  tempera- 
ture that  the  expansion  of  the  mercury  will  not  cause 
it  to  leak  out,  as  is  sometimes  supposed. 

The  direct  current  Sangamo  meter  cannot  be  used 
on  alternating  current  circuits  because  of  the  high  self- 
inductance  of  the  potential  winding.  Therefore,  if 
alternating  current  be  applied  to  a  direct  current  meter 
very  little  current  would  pass  through  the  potential 
coil,  and  even  that  would  lag  by  so  many  degrees  that 
it  would  produce  a  very  small  torque. 

Fig.  62  shows  diagramatically  the  Sangamo  direct 
current  meter.  The  damping  system  in  this  type  of 
meter  is  essentially  the  same  as  previously  explained 
in  connection  with  induction  and  commutating  types 
of  meters.  In  the  above  figure  the  damping  magnets 
are  shown  at  M,  and  the  damping  disc  at  D.  The 
copper  terminals  which  lead  the  current  into  the 
mercury  and  thence  to  the  disc,  A,  are  shown  at  EE. 
The  external  resistance,  R,  is  in  series  with  the  poten- 


MERCURY    FLOTATION  91 

tial  winding,  SC.  The  light  load  adjustment  is  made 
by  moving  the  slider,  K,  to  the  right  or  left,  thereby 
causing  part  of  the  shunt  current  passing  through  the 
potential  winding  to  flow  through  the  armature.  This 
current  reacting  writh  the  magnetic  field  from  the 
potential  winding  produces  a  no-load  torque  which  is 
sufficient  to  compensate  for  friction. 

The  torque  of  the  Sangamo  meter  is  very  low.  the 
torque  of  a  5  ampere  direct  current  meter  being  only 
about  20  gram-millimeters.  It  may  be  said,  however, 
that  in  the  case  of  the  mercury  flotation  meter  the  pres- 
sure on  the  jewel  bearing  is  relatively  small,  and  it  is 
therefore  not  necessary  to  have  as  high  a  torque  as  in 
other  types.  The  reason  for  this  low  torque  in  the  San- 
gamo meter  is  due  to  the  fact  that  the  armature  is  equiv- 
alent to  only  one  turn,  and  as  it  is  not  practicable  to 
carry  more  than  8  or  TO  amperes  through  the  armature, 
the  effective  armature  turns  will  necessarily  be  low. 
Current  shunts  are  used  in  all  direct  current  Sangamo 
meters  having  a  capacity  of  more  than  10  amperes,  the 
shunt  being  external  in  large  capacity  meters  and 
internal  in  the  smaller  sizes.  The  sliding  connector,  S, 
shown  in  Fig.  62  is  used  for  adjusting  the  armature 
current  with  respect  to  the  shunts. 

It  is  not  feasible  to  build  the  mercury  meter  for 
three-wire  direct  current  service,  since  it  would  neces- 
sitate the  construction  of  two  separately  insulated 
mercury  chambers  and  armatures,  which  would  of 
course  be  too  bulky,  complicated  and  expensive  to  be 
warrantable.  Two  mercury  meters  have  to  be  used 
where  it  is  desired  to  measure  the  power  in  a  three- 
wire  direct  current  circuit,  with  this  type  of  instru- 
ment. 

The  alternating  current  meter  of  this  type  is 
shown  diagramatically  in  Fig.  63.  As  will  be  noted, 
the  armature  circuit  is  in  shunt  with  the  source  of 
supply  in  this  case,  as  was  above  mentioned,  rather 
i-han  in  series  as  is  the  case  with  the  direct  current 
tvpe  The  small  potential  transformer,  N,  has  its 
primary,  PT,  connected  across  the  line  and  induces 


'•92 


THE    WATTHOUR    METER 


through  its  secondary,  MS,  a  current  of  high  amperage 
-and  very  low  e.m.f.  This  current  flows  directly 
through  the  armature  as  is  shown.  The  actual  value 
•of  this  secondary  current  is  between  12  and  20  amperes 


T 

F 

Fig.  63. 


-•at  an  e.m.f.  of  approximately  0.05  volt.  The  trans- 
former also  has  an  auxiliary  secondary  winding,  AS, 
the  terminals  of  which  are  connected  through  the 
variable  resistance,  RR,  to  the  light  load  adjusting 
-coil,  J,  which  is  wound  on  the  same  core  with  the  series 


MERCURY    FLOTATION  93 

field  coils,  FC.  By  moving  the  slider,  K,  along  the 
resistance  the  compensating  effect  of  the  light  load 
adjustment  may  be  varied  to  allow  for  friction. 

The  full  load  adjustment  in  the  Sangamo  meter  is 
quite  different  from  the  usual  practice,  in  that  the 
damping  effect  of  the  retarding  magnets  is  varied  by 
"shunting"  more  or  less  of  the  magnetic  lines  through 
a  soft  iron  disc,  H  (Figs.  62  and  63),  which  is  placed 
directly  above  the  magnet  system,  rather  than  by 
moving  the  magnets  themselves.  This  soft  iron  disc 
is  movable  in  a  vertical  direction  as  shown  ;  by  bring- 
ing it  in  close  proximity  of  the  magnets,  it  weakens 
their  effect,  thereby  causing  the  meter  to  run  faster. 

The  Ampere-Hour  Meter. 

The  Sangamo  ampere-hour  meter,  is  now  being 
used  quite  frequently  in  connection  with  the 
charging  and  discharging  of  storage  batteries.  Storage 
batteries  are  rated  on  their  ampere-hour  capacity,  and 
it  will  therefore  be  seen  that  an  instrument  which  will 
indicate  the  amount  of  current  that  has  been  stored  in, 
or  the  amount  of  current  remaining  in  a  battery  is  a 
valuable  accessory  to  the  electric  automobile  garage, 
or  in  fact  to  any  one  having  the  care  of  a  storage 
battery. 

The  construction  of  the  Sangamo  ampere-hour 
meter  is  essentially  the  same  as  that  of  the  watthour 
meter,  except  that  the  exciting  electro-magnet  is  re- 
placed with  a  powerful  permanent  magnet.  The  turn- 
ing effort  of  the  armature  will  therefore  be  independent 
of  the  potential  of  the  circuit  on  which  the  meter  is 
used,  being  directly  proportional  to  the  current  passing 
through  it.  This  type  of  meter  is  usually  furnished 
with  a  single  pointer,  which  will  show  at  a  glance  the 
condition  of  the  battery  with  respect  to  the  charge  or 
discharge.  The  dial  may  be  furnished  with  a  movable 
contact,  which  by  means  of  a  relay  can  be  made  to 
open  the  main  circuit  through  a  "shunt-trip"  type  of 
circuit-breaker;  this  movable  contact  can  be  set  so  as- 
to  open  the  circuit  at  any  predetermined  value. 


94 


THE    WATTHOUR    METER 


Connections. 

A  few  representative  connections  of  the  Sangamo 
meter  are  shown  in  the  following  figures : 


Fig.  64. 

Two-Wire  D.  C.  Meters — lie  to 
250  volts;  100  to  400  amperes, 
inclusive,  box  type  "Current 
Shunt."  New  "Pocket  Type" 
Shunt  used  in  capacities  100 
to  200  amperes,  inclusive, 
except  for  street  railway 
service. 


Fig.  67. 

Three-Wire  Alternating  Me- 
ters— 110-220  volts  single- 
phase;  capacities  200  am- 
peres per  side  and  over. 
With  Current  Transformer 
having  two  primary  wind- 
ings. 


if 

© 
J  1 

OOOO 

1            1 

n^l                                              «-^»  1 

N0d=) 

c    IN       SHUNT    OuTg 

^ 

Fig.  65. 


Fig.  66. 


Two-Wire  Meters — 110  and  220  volts,  for  A.  C. 
Meters  5  to  100  amperes;  D.  C.  meters  5  to  80 
amperes,  inclusive.  Meters  may  be  connected 
according  to  Fig.  65  or  Fig.  66,  but  the  former 
is  preferable,  as  this  method  prevents  tamper- 
ing with  the  meter  connections. 


MERCURY    FLOTATION 


95 


LINE 


LINE 


Fig.  68. 

Service  type,  ampere-hour  me 
ter,  10  to  100  amperes  inter- 
nally shunted. 


Fig.  69. 

'Auto"  type,  ampere-hour  me- 
ter, with  contact  device  and 
auxiliary  circuit  for  tripping 
a  circuit-breaker.  Capacity 
10  to  100  amperes. 


CHAPTER  VI. 
MISCELLANEOUS. 

The  Pre-Payment  Watthour  Meter. 

The  prepayment  device  as  applied  to  the  gas 
meter  has  demonstrated  its  usefulness  after  a  number 
of  years  of  service,  it  being  especially  valuable  in 


Fig.  73. 

cities  where  many  of  the  consumers  are  transient  resi- 
dents, and  also  where  those  served  find  it  a  burden 
to  make  the  usual  monthly  payments,  preferring  to 
pay  as  occasion  demands.  The  slow7  introduction  of 
prepayment  electric  meters  has  been  partly  due  to  the 
limited  demand,  because  usually  the  class  of  people 
that  have  been  using  electricity  for  light,  power,  heat- 
ing and  cooking  have  not  been  of  the  kind  that  would 


MISCELLANEOUS 


97 


desire  or  that  would  necessitate  the  installation  of  pre- 
payment meters.  Now  electricity  occupies  such  a 
broad  field  that  it  may  be  said  to  be  used  by  all  classes 
of  people,  therefore  the  distributing  company  is  often 
confronted  with  the  problem  of  "slow  pay"  customers. 
Especially  is  this  true  with  small  commercial  estab- 
lishments, such  as  the  poorer  classes  of  restaurants, 
saloons,  tailor  shops,  etc.  The  prepayment  meter 


Fig.   74. 

when  installed  in  such  places  will  oftentimes  obviate 
difficulties  which  may  otherwise  arise. 

The  prepayment  device  can  be  furnished  either  as 
an  integral  part  of  the  watthour  meter,  or  as  a  sep- 
arate device.  The  construction  and  operation  in  either 
case  is  essentially  the  same,  except  that  in  the  former 
case  the  connection  to  the  meter  is  mechanical  and  in 
the  latter  case  it  is  electrical.  Fig.  73  illustrates,  the 
prepayment  device  attached  directly  to  the  watthour 
meter,  in  which  case  a  pinion  in  the  registering  mech- 
anism of  the  meter  meshes  directly  with  the  debiting 


98  THE   WATTHOUR    METER 

mechanism  of  the  device.  In  case  the  prepayment 
device  is  used  separately  from  the  watthour  meter, 
the  debiting  mechanism  is  controlled  by  an  electro- 
magnet which  is  connected  directly  in  the  line,  con- 
tact being  made  through  suitable  gears  and  commu- 
tating  device  in  the  meter  register. 

Fig.  74  shows  the  prepayment  device  when  used 
as  a  separate  part  of  a  watthour  meter. 

Construction  and  Operation. 

The  small  knob  shown  protruding  from  the  front 
of  the  case  is  provided  with  a  slot  for  the  reception  of 
coins  of  the  proper  denomination.  After  the  coin  is 
placed  in  the  slot  the  knob  is  given  a  half  turn  to  the 
right,  the  coin  engaging  the  shaft  of  the  crediting 
mechanism  and  the  main  circuit  being  simultaneously 
closed.  The  coin  is  carried  around  with  the  turn  of  the 
knob  and  released  into  a  chute  which  conveys  it  to  a 
coin  chamber  in  the  base  of  the  meter.  The  first  coin 
placed  in  the  slot  will  cause  the  indicating  hand  to 
move  to  the  figure  "i"  on  the  crediting  dial,  the  sec- 
ond coin  will  cause  the  hand  to  move  to  the  figure 
"2,"  and  so  on,  provision  usually  being  made  to  accom- 
modate twelve  quarter  dollar  coins  at  once.  Thus 
$3.00  worth  of  current  may  be  paid  for  in  advance,  and 
as  each  quarter's  worth  is  used,  the  debiting  mechan- 
ism will  cause  the  indicating  hand  to  recede  to  the  next 
figure.  The  dial,  therefore,  only  indicates  the  number 
of  coins  to  the  credit  of  the  consumer  and  does  not 
take  into  account  the  coins  for  which  energy  has  al- 
ready been  delivered.  The  total  number  of  coins 
placed  in  the  device  can  always  be  readily  translated 
from  the  watthour  register  by  multiplying  the  reading 
in  kilowatt  hours  by  the  rate  per  kilowatt  and  divid- 
ing the  result  by  the  denomination  of  the  coin.  When 
all  the  energy  which  has  been  paid  for  has  been  de- 
livered, the  crediting  hand  moves  back  to  the  zero 
position  and  opens  an  internal  switch,  which  cannot 
be  again  closed  until  another  coin  is  deposited.  The 
switch  contacts  are  made  of  laminated  copper  strips 
which  insure  good  electrical  contact. 


MISCELLANEOUS  99 

The  force  which  actuates  the  debiting  device  con- 
sists of  a  large  spiral  spring.  This  spring  exerts  prac- 
tically a  constant  force,  since  it  is  so  designed  that  it 
is  always  operating  under  a  low  percentage  of  its 
maximum  tension.  The  gearing  mechanism  of  the 
spring  is  "differential"  in  operation,  so  that  the  escape- 
ment is  independent  of  the  knob.  This  permits  the 
consumer  to  place  more  coins  in  the  device  before  all 
energy  paid  for  has  been  delivered,  without  in  any 
way  disturbing  the  crediting  and  debiting  mechanism. 
The  prepayment  device  is  usually  made  for  rates  rang- 
ing from  5  to  20  cents  per  kilowatt-hour  in  steps  of 
one-half  cent.  Each  prepayment  device  is  marked 
with  the  rate  per  kilowatt-hour  with  which  it  should 
be  used ;  if,  however,  it  is  desired  to  change  this  rate 
of  charge  it  is  only  necessary  to  change  the  gear  ratio 
of  the  "rate  device,"  the  construction  being  such  that 
this  is  easily  accomplished.  The  coin  receptacle  is  in 
the  back  of  the  meter  and  so  located  and  protected 
that  the  meter  cover  may  be  removed  (for  testing  and 
inspection),  without  giving  access  to  the  coin  recep- 
tacle. It  consists  of  a  drawer  which  can  be  slipped  in 
or  out  from  the  bottom  of  the  meter  case,  so  that  it 
is  not  necessary  for  the  collector  to  remove  the  meter 
cover  when  taking  out  the  coin.  Lugs  (as  will  be 
seen  from  the  illustration)  are  furnished  so  that  the 
coin  receptacle  can  be  locked  by  means  of  a  suitable 
padlock. 

The  manufacturing  companies  have  perfected  the 
prepayment  device  to  such  a  degree  that  it  is  as  trust- 
worthy as  the  gas  meter  device,  and  they  have  de- 
signed it  so  that  "beating"  is  practically  impossible. 
When  a  coin  is  once  placed  in  the  slot,  the  knob  can- 
not be  turned  back  until  a  half  'turn  has  been  com- 
pleted and  the  coin  has  dropped  into  the  chute.  A 
coin  of  smaller  dimensions  than  that  for  which  the 
slot  is  designed  will  not  allow  the  knob  to  be  turned. 
The  credit  knob  is  provided  internally  with  a  sharp 
edge  which  will  shear  off  any  thread  or  fine  wire  that 
may  have  been  attached  to  the  coin  with  fraudulent 
intentions. 


100  THE   WATTHOUR   METER 

The  prepayment  attachment  for  the  electric  meter 
has  the  advantage  over  the  gas  device  in  that  it  may 
be  placed  at  any  point  remote  from  the  meter  which 
it  controls.  The  electric  meter  may  be  in  the  attic, 
the  basement  or  on  the  back  porch,  and  the  prepay- 
ment device  in  the  kitchen  or  other  convenient  place. 

The  diagrams,  Fig.  75,  show  the  connections  of 
the  prepayment  device  above  described  \vhen  used 
in  connection  with  alternating  and  direct  current  watt- 
hour  meters  as  manufactured  by  the  General  Electric 
Company. 

The  Wright  Demand  Indicator. 

The  need  of  an  instrument  which  will  indicate  the 
maximum  demand  made  upon  the  current  supply  of  a 
distributing  company  has  lead  to  the  development  of 
the  device  shown  in  Fig.  76,  which  is  known  as  the 
"Wright  Demand  Indicator."  As  will  be  noted  from 
Chapter  VIII,  relative  to  rates,  the  cost  of  serving  a 
customer  whose  average  load  for  24  hours,  compared 
with  his  maximum,  is  high,  will  be  lower  than  the  cost 
of  serving  a  customer  the  ratio  of  whose  average  to 
maximum  load  is  low.  In  other  words,  the  customer 
with  a  good  "load  factor"  is  more  profitable  to  the 
distributing  company.  For  example,  suppose  that  a 
given  customer  has  a  connected  load  of  lamps  amount- 
ing to  10  kw.  which  are  being  supplied  with  current 
for  only  two  hours  in  the  evening,  and  suppose  that 
another  customer  has  a  connected  load  of  motors 
amounting  to  2  kw.  that  takes  current  for  ten  hours. 
In  either  case,  the  kilowatt-hours  per  day  are  the 
same,  but  the  lighting  load  comes  when  the  demand 
upon  the  station  is  at  the  highest  point ;  whereas,  the 
motor  customer  is  being  served  when  the  generating 
machinery  would  otherwise  be  running  partially 
loaded.  It  is  therefore  evident  that  the  customer 
whose  demand  is  practically  constant,  such  as  the 
motor  customer,  is  the  most  profitable,  and  is  entitled 
to  a  better  rate. 

The  Wright  Demand  Indicator  can  be,  and  is 
used  to  great  advantage  in  determining  the  maximum 


MISCELLANEOUS 


101 


O 


D 


[0° 

x.                               J 

n> 
J 

D 

V 

-  1 

1 

^ 

p_ 

? 

V 

rF 

—  > 

I 

0  ° 

ts 

D 

§> 

I 

I 

—  ' 

, 

II1  

c 

102  THE   WATTHOUR    METER 

load  on  transformers.  Its  systematic  use  in  determin- 
ing the  actual  maximnm  loads  on  the  transformers 
of  a  distributing  system  will  insure  the  transformers 
against  excessive  overloads.  As  is  the  case  with 
meters,  it  is  not  infrequent  that  transformers  of  too 
large  a  capacity  are  used  for  supplying  a  given  con- 
nected load ;  the  maximum  demand  indicator  is  valu- 
able in  determining  the  proper  capacity  of  distributing 
transformers.  The  indicator  may  be  mounted  on  the 
pole  and  connected  in  the  circuit  by  replacing  one  of 
the  primary  fuse-plugs  with  the  plug  having  loose 
connections  which  are  attached  to  the  terminals  of  the 
indicator.  When  the  indicator  is  used  in  this  way 
it  should  be  mounted  on  a  suitable  board,  which  will 
facilitate  handling  and  also  prevent  breakage.  The 
indicator  can  also  be  applied  to  motors  driving  ma- 
chine tools,  etc.,  to  ascertain  whether  or  not  they  are 
being  operated  in  excess  of  their  guarantees. 

Around  the  upper,  or  left  hand  bulb,  shown  in 
Fig.  76,  and  in  close  thermal  contact  with  it,  is  a  band 
of  resistance  wire  through  which  passes  the  main  line 
current  or  a  proportionate  part  thereof;  shunts  being 
provided  with  high  capacity  direct  current  indicators, 
and  current  transformers  with  the  larger  sizes  for  use 
on  alternating  current  circuits.  The  current  in  pass- 
ing through  the  resistance  band  heats  the  air  in  the 
glass  bulb,  which  in  turn  causes  the  air  to  expand, 
thereby  forcing  the  liquid  up  into  the  right-hand  tube, 
the  liquid  then  falling  into  the  central  or  index  tube, 
which  is  set  in  front  of  the  scale.  The  heat  generated 
in  the  resistance  band  is  proportional  to  the  square 
of  the  current  passing  through  it  (watts  dissipated  in 
resistance  =  resistance  X  the  square  of  the  current 
flowing). 

The  difference  in  temperature  of  the  air  in  the 
two  bulbs  causes  the  liquid  to  flow  as  it  does,  and 
since  any  external  temperature  affects  the  air  in  the 
two  bulbs  similarly,  no  error  will  result  due  to  changes 
in  temperature  of  the  surrounding  air. 

The  tube  is  reset  by  simply  tilting  it  and  allowing 
the  liquid  to  flow  out  of  the  index  tube  back  in  to  the 


MISCELLANEOUS 


103 


Fig.  77. 


Fig.  76, 


Fig.  78. 


104  THE   WATTHOUR    METER 

U  tube.  In  resetting  the  indicator,  air  bubbles  from 
one  arm  of  the  U  may  be  carried  over  into  the  other 
arm,  thereby  unequalizing  the  pressure  and  causing  the 
calibration  to  be  disturbed.  To  prevent  this  trouble, 
the  little  traps  shown  in  the  illustration  are  located 
in  the  bottom  of  the  U,  and  when  the  tube  is  inverted 
(or  partially  so),  they  remain  covered  with  the  liquid, 
clue  to  the  action  of  the  capillaries  in  the  channels 
of  the  U  tube,  and  thereby  prevent  the  passage  of  air 
from  one  side  of  the  U  to  the  other  side. 

The   Induction  Type  Watt   Demand  Indicator. 

The  Wright  Demand  Indicator  which  has  just 
been  described  deals  with  the  current  only,  and  does 
not  take  into  consideration  the  power  factor  of  the 
circuit  on  which  it  is  used  nor  fluctuations  in  line  volt- 
age. It  is  often  necessary  to  know  the  maximum  watt 
demand,  especially  in  the  case  of  motor  installations. 
To  fulfill  the  requirement  of  such  a  device  the  General 
Electric  Company  has  designed  the  instrument  shown 
in  Fig.  78,  which  is  known  as  the  "Polyphase  Maxi- 
mum Watt  Demand  Indicator."  This  instrument  will 
indicate  and  register  the  maximum  watt  demand  on 
single,  two  or  three  phase  systems  having  a  balanced 
or  an  unbalanced  load,  and  irrespective  of  the  power 
factor  and  voltage  fluctuations. 

This  type  of  indicator  is  simply  a  modification  of 
the  polyphase  watthour  meter,  the  ordinary  retarding 
magnets  being  replaced  by  a  greater  number  of  very 
powerful  permanent  magnets  arranged  as  shown,  and 
with  both  electrical  elements  acting  on  the  upper  disc. 
The  register  as  ordinarily  furnished  on  watthour 
meters  is  replaced  by  a  circular  scale  having  two  con- 
centric pointers,  one  of  which  is  connected  to  the  disc 
shaft  through  a  suitable  train  of  gears ;  the  other 
pointer  being  driven  by  the  first  pointer.  As  the  load 
on  the  indicator  causes  the  first  pointer  to  deflect,  the 
second  pointer  is  carried  to  the  maximum  position 
reached  by  the  first  pointer,  in  which  position  it  is  held 
by  a  ratchet. 

The  upper,  or  "motor"  disc  is  opposed  and  con- 


MISCELLANEOUS 


1.05 


trolled  by  phosphor-bronze  springs  which  confine  the 
rotation  of  the  disc  to  a  definite  number  of  revolu- 
tions. The  torque  acting  on  the  disc  is  proportional 
to  the  power  passing  through  the  indicator,  therefore 
by  using  a  control  spring  of  many  convolutions,  the 
graduation  of  the  scale  can  be  made  uniformly. 

A  curve  showing  the  relation  of  the  percentage  of 
deflection  to  the  time  during  which  it  takes  the  pointer 
to  reach  such  deflection  is  shown  in  Fig.  79.  It  will 
be  noticed  that  the  curve  rises  very  rapidly  until  the 
90%  position  is  reached,  and  that  the  time  from  90% 


Fig.  79. 

to  1 00%. is  relatively  great;  for  this  reason  the  indi- 
cators are  usually  rated  by  defining  the  time  lag  as 
the  interval  of  time  taken  to  record  90%  of  any  change 
in  load.  The  time  lag  depends  upon  the  torque  of  the 
electrical  element  and  upon  the  retarding  effort  of  the 
permanent  magnets ;  by  altering  the  effect  of  these 
two  factors,  a  time  lag  from  one  to  thirty  minutes  can 
be  secured.  By  changing  the  position  of  the  retarding 
magnets  in  an  indicator  having  a  definite  rating,  the 
time  lag  may  be  varied  from  ior^  to  15%. 

The  polyphase  maximum  watt  demand  indi- 
cator can  be  used  on  single  phase  circuits  by  connect- 
ing the  potential  coils  in  multiple  and  the  current  coils 
in  series  and  "dividing  the  scale  deflection  by  two. 


CHAPTER  VII. 
MAINTENANCE  AND  TESTING. 

The  care  and  maintenance  of  recording  watthoui 
meters  should  receive  the  most  careful  attention  from 
distributing  companies,  and  only  competent  men 
should  be  placed  in  charge  of  the  meter  department 
because,  as  pointed  out  in  Chapter  I,  negligence  in  the 
proper  care  of  the  meter  system  may  result  in  a  serious 
financial  loss.  It  is  therefore  essential  that  the  dis 
tributing  company  be  equipped  to  test  and  make  minoi 
adjustments  of  its  meters.  In  order  to  secure  the  best 
results  it  is  necessary  that  some  systematic  method  of 
inspecting  and  testing  be  adopted.  Almost  all  of  the 
larger  companies,  realizing  the  importance  of  metei 
accuracy,  have  separate  and  well-organized  meter  de 
partments  which  are  equipped  for  testing,  repairing 
and  re-calibrating  service  meters,  this  department 
being  held  responsible  for  their  proper  operation. 

With  small  companies  it  is  often  impractical  to 
have  a  separate  meter  department,  but  it  will  be 
found,  even  by  the  smallest  distributing  companies 
that  it  is  economy  in  the  end  to  have  some  systematic 
method  of  testing  and  caring  for  meters.  In  small 
stations,  where  the  size  of  the  system  so  warrants,  it 
is  advisable  to  employ  the  entire  time  of  at  least  one 
man  to  see  that  the  meters  are  kept  in  proper  con 
dition ;  where  this  is  not  warrantable,  it  can  usually  be 
arranged  to  have  the  same  man  do  all  of  the  metei 
work,  rather  than  having  two  or  three  men,  each  doing 
a  part  of  it,  because  where  there  is  one  man,  the 
responsibility  is  then  definitely  placed,  and  further- 
more, he  becomes  more  efficient  and  he  will  usually 
take  more  interest  and  pride  in  seeing  that  his  meters 
are  always  in  the  best  of  condition. 


MAINTENANCE  AND  TESTING 


107 


Reading  the  Meter  and  Keeping  of  Records. 

The  interval  between  the  readings  of  each  indi- 
vidual meter  should  be  as  nearly  uniform  as  possible, 
because  if  the  interval  is  greater  for  one  month  than 
it  is  for  the  next,  the  customer's  bill  will  as  a  rule  be 


Kind... 
Style.. 
Cycle 


.Set -..Motors K.W.. 

..Tested Inc Are 

Amp Volt  Conit. 


Folio — 

.Route 

No 

Rate 


Date  Reed 


DEC. 


Fig.  80. 


108  THE   WATTHOUR    METER 

correspondingly  affected,  which  will  in  a  great  many 
cases  lead  to  dissatisfaction  on  the  part  of  the  con- 
sumer, with  the  resulting  annoyance  and  explanations 
necessary  on  the  part  of  the  distributing  company. 
The  best  way  in  which  to  obviate  such  troubles,  and 
to  insure  a  uniformity  of  meter  reading  is  to  begin 
each  month  at  a  fixed  date  and  always  have  the  meter- 
reader  go  over  the  route  in  the  same  order. 

In  reading  meters  it  is  usual  practice  to  have  a 
special  form  of  "loose-leaf"  book  which  has  on  each 
page  twelve  (or  six)  facsimile  prints  of  the  meter  dial, 
upon  which  can  be  marked  the  corresponding  position 
of  the  pointers.  Such  a  card  is  reproduced  in  Fig.  80. 
the  reverse  side  of  the  card  being  used  for  any  notes 
\vhich  may  be  necessary.  The  meter  reader  should 
first  note  the  actual  reading  of  the  meter  and  put 
the  figures  down  in  the  column  set  aside  for  this 
purpose :  he  should  then  copy  the  exact  positions  of 
all  of  the  pointers.  By  taking  both  readings  thus, 
one  acts  as  a  check  on  the  other,  and  with  a  little 
practice  a  man  becomes  efficient  and  accurate. 

Some  distributing  companies  use  the  form  shown  in 
Fig.  81,  which  does  not  provide  for  the  check  afforded 
by  having  both  the  direct  reading  and  the  positions  of 
the  pointers  copied.  There  is  a  great  difference  of 
opinion  as  to  the  most  advantageous  method  of  tran- 
scribing the  meter  readings  to  the  record  book.  The 
objections  advanced  against  the  method  of  copying 
the  positions  of  the  meter  pointers  is  the  fact  that  it 
takes  considerably  more  time  than  it  does  to  simply 
transcribe  the  numerical  value  direct ;  it  also  involves 
more  work  on  the  part  of  the  book  keeping  orga- 
nization, and  there  is  also  liability  of  error  when  the 
book-keeper  transcribes  the  reading  from  the  meter 
reader's  book  to  the  record  book. 

The  method  of  simply  transcribing  the  reading 
numerically  is  undoubtedly  the  most  rapid  and  the 
most  satisfactory  if  a  well  experienced  and  careful 
man  can  be  employed  for  this  work,  but  the  method 
of  transcribing  numerically  and  also  copying  the  po- 


MAINTENANCE  AND  TESTING 


109 


sitions  of  the  pointers  is  usually  to  be  preferred  on 
account  of  the  check  which  it  affords. 

Figure  82  represents   a  very  convenient  form  of 
file-card  which  may  be  used  for  the  office  records  and 

Our  No C Mfgrs.  No. 

Location  of  Meter... 


DATE 
READ 

READING 

READ  BY 

JUNE 

JULY 

FORWABDBD                                  KW 
KW 

AUG 

KW 

SEPT. 

KW 

OCT. 

KW 

NOV. 

KW 

DEC. 

KW 

JAN. 

KW 

FEB.. 

KW 

MAR. 

KW 

APR. 

KW 

MAY 

KW 

JUNE 

KW 

Fig.  81. 

to  which  the  figures  from  the  reader's  book  are  trans- 
ferred ;  the  reverse  side  of  the  card  is  similar  and  the 
record  may  be  continued  thereon.  Under  no  condi- 
tions should  the  record  cards  be  taken  from  the  files. 


THE   WATTHOUR   METER 


SONIQV3H  1N31IS 


MAINTENANCE  AND  TESTING 

METER  TEST  REPORT. 

Request  Date,. 


111 


Size. . 


Name 

Address 

Location  of  Meter. . 

Company  No. 

Mfgr.  No.: . 

Make Type 

Testing  Constant Reading  Constant. 

I 


.  .Amps. 

Wires 

..  Volts 


%  Slow 

%  Fast 

%  Slow 

....    %  Fast 

\  Load 

f  Load 

|Load 

Full  Load 

2  Cp.    |    4  Cp.    j    8  Cp.    I  16    Cp.  |    32  Cp.    j     Arcs     j     Fai 


Misc. 


Remarks: 


Date    Meter    Tested 


Meter  Tester. 

N.  B.—If  these  Requests  fail  to  follow  in  Numerical  Order  promptly 
advise  Accounting  Department 

Fitr.  83a. 


112 


THE    WATTHOUR    METER 


It  is  not  infrequent  that  check  readings  have  to 
be  made,  sometimes  at  the  request  of  the  consumer 
and  sometimes  because  of  apparent  discrepancies  in 
the  monthly  reading.  When  such  readings  are  taken 
it  is  advisable  to  use  a  "re-read"  card  of  a  form  similar 
to  that  shown  at  (b)  in  Fig.  83.  Fig.  83  (a)  shows  a 
convenient  form  of  record  blank  for  use  in  testing 
meters. 


Foiio 
Line 


RE-READ  METER 


L'M-D&Co— 8-08 


Date  issued . 


Reading 


Address 

Watt  Hrs _ 

K.   \V..  .. 


Meter  Number 
Date  Read 


_ Constant. 

- By 

(Tse  back  of  this  slip  for  remarks  ) 

Fig.  83b. 


During  the  regular,  or  periodic,  testing  of  service 
meters,  there  will  invariably  be  found  a  number  of 
slow  meters  and  it  is  good  policy  to  use  a  card  sim- 
ilar to  Fig.  84,  so  that  the  consumer  may  expect  the 

DEAR  SIR  : 

Your  meter  located  at... _.. 

being  our  No upon  being  tested  has  been  found c/c 

slow.      Fearing  that  any  additional  billing  on  your  previous  consumption 
would  be  inaccurate,  and  possibly  unjust  to  you,  we  are  not  rendering  any 
additional  bill,  but  are  standing  whatever  loss  has  been  incurred. 
We  trust  all  this  is  satisfactory. 

Yours  truly, 
Fig.  84. 


MAINTENANCE  AND  TESTING 


113 


next  bill  to  vary  from  the  last  one.  Such  precautions 
involve  very  little  time  and  expense,  and  in  many 
cases  they  save  heated  arguments  and  preserve  the 
good  will  of  the  consumer. 


Date  Tested  .....Testing  Const  
%l              %J 

Dafe  Rec'd  Testing  Const  
%l               %l 

POUND 

LBFT 

POUND 

LEFT 

•  t/ 

% 

% 

J/2 

Full 



Full 

Date  Tested  Testing  Const  

%l           %£ 

Date  Rec'd  Testing  Const  __  
,  %l              %l 

FOUND 

LEFT 

POUND 

LEFT 

V4 

% 

_^_ 
Full 



Vz 



Full 

Date  Tested  Testing  Const  „  

-  %l           -  %S 

Date  Rec'd  Testing  Const  
%l              %\ 

FOUND 

LEFT 

POUND 

LEFT 

'/4 

y4 
JL 

Full 





'/* 



Full 

Fig.  85a. 
ELECTRIC 'METER    RECORD. 


OUR  NO. 

MANUFACTI-RT 

.It's  No.j           MAKE 

TYP 

E 

DATE  SET 

READING 

NAME 

ADDRESS 

DATE  OUT 

READING 

' 

Fig.  85b 


Too  much  stress  cannot  be  laid  upon  the  syste- 
matic keeping  of  the  data  regarding  the  individual 
performance  of  the  meters,  and  for  this  purpose  it  is 
advisable  to  keep  record  cards  similar  to  that  shown 
in  Fig.  85,  (a)  being  the  front  side  and  (b)  being 


114  THE    WATTHOUR    METER 

the  reverse  side.  Such  data  will  give  an  accurate  and 
ready  insight  into  the  continued  performance  of  the 
individual  meters,  and  will  act  as  a  guide  in  the 
future  selection  of  the  best  meter  for  the  service  of 
the  existing  conditions. 

Installation  of  Meters. 

With  few  exceptions,  new  meters  will  be  found 
to  be  well  within  the  limit  of  good  accuracy,  inas- 
much as  they  are  carefully  tested  and  adjusted  at  the 
factory  before  they  are  shipped.  Before  a  meter  is 
installed,  however,  its  accuracy  should  be  checked 
as  a  matter  of  record  and  in  order  to  make  any  minor 
adjustments  that  may  be  found  to  be  necessary.  (In 
transporting  a  meter  from  place  to  place  it  is  not  at 
all  unlikely  that  the  finer  adjustments  may  be  af- 
fected.) When  installing  a  meter  care  should  be 
taken,  as  far  as  possible,  to  select  an  easily  accessible 
place  which  is  free  from  vibration,  jar  and  moisture, 
and  a  place  where  it  will  be  protected  from  the 
weather;  it  should  be  installed  in  such  a  position  that 
it  can  be  easily  read — a  point  which  is  too  often  over- 
looked. The  meter  should  not  be  roughly  handled 
during  installation  or  in  carrying  it  from  place  to 
place,  as  it  must  be  remembered  that  it  is  a  delicate 
device  and  should  be  handled  accordingly. 

W^hen  putting  a  meter  into  service  care  should 
be  taken  to  see  that  the  moving  element  does  not 
rest  on  the  jewel  bearing  until  it  is  installed  and 
ready  for  operation.  The  different  makes  of  meters 
have  different  methods  of  accomplishing  this  result, 
but  in  all  of  them  provision  is  made  for  protecting 
the  jewel  bearing  during  transportation. 

Before  a  service  meter  is  put  into  operation  it  is 
necessary  to  see  that  it  is  level,  since  friction  is 
liable  to  result  if  this  precaution  is  not  taken.  (Some 
manufacturers  furnish  a  small  pocket  spirit  level  for 
this  purpose). 

Meters  should  never  be  located  beneath  water 
pipes  nor  near  steam  pipes ;  they  should  be  placed 


MAINTENANCE  AND  TESTING  115 

within  8  feet  of  the  floor  line  so  that  the  periodic 
testing  may  be  accomplished  with  the  greatest  ease. 

Meters  should  not  be  placed  closer  together  than 
15  inches  between  centers;  if  placed  closer  than  this 
they  may  "interfere"  with  each  other  through  the 
effects  of  stray  fields. 

Meters  should  not  be  installed  close  to 
conductors  carrying  heavy  currents  nor  in  the  vicin- 
ity of  iron  girders  or  posts. 

The  subject  of  "over-metering"  has  already  been 
mentioned  in  several  places;  as  a  general  rule  it  may 
here  be  stated  that  for  residence  lighting  the  meter 
should  have  a  capacity  of  approximately  50  per  cent 
of  the  connected  load ;  for  small  store  lighting,  win- 
dow lighting,  out-door  multiple  arc  lamps,  etc.,  the 
meter  should  have  a  capacity  of  about  90  per  cent 
to  100  per  cent  of  the  connected  load,  while  for 
medium  and  large  sized  stores  this  percentage  will  be 
approximately  75  to  80  per  cent.  For  metering  a 
motor  load,  the  meter  should  usually  have  a  capacity 
of  100  per  cent,  except  where  a  number  of  motors 
are  installed,  some  of  which  may  be  running  idle  or 
lightly  loaded  most  of  the  time,  in  which  case  a 
smaller  meter  could  be  used.  Occasionally  it  is 
necessary  to  install  a  meter  having  a  greater  capacity 
than  the  connected  motor  load,  as  for  instance  in  the 
case  of  hoists  and  high  speed  elevators. 

A  very  convenient  and  reliable  method  of  level- 
ing meters  without  the  use  of  a  spirit-level  consists 
of  placing  a  coin,  such  as  a  quarter  of  a  dollar,  on 
the  front  of  the  disc  and  as  near  to  the  edge  as 
possible ;  if  the  meter  is  out  of  "plumb,"  the  disc  will 
move  so  as  to  bring  the  coin  toward  the  side  which 
is  the  lowest.  The  meter  can  then  be  leveled  so 
that  the  disc  will  remain  stationary  with  the  coin 
resting  on  the  front  edge ;  the  coin  should  then  be 
placed  on  the  edge  of  the  disc  in  a  position  ninety 
degrees  from  its  former  position,  and  the  meter  then 
leveled  from  front  to  back,  without  changing  the  pre- 
vious adjustment.  When  the  disc  is  perfectly  level, 


116  THE   WATTHOUR    METER 

the   coin   can   be   placed   at   any   position   around   the 
edge,  and  the  disc  will  remain  stationary. 

Precaution  should  be  taken  to  see  that  the  meter 
is  connected  properly  into  the  circuit,  so  that  it  will 
rotate  in  the  right  direction,  especially  is  this  true 
with  polyphase  meters,  and  with  single,  phase  meters 
when  used  to  measure  polyphase  power.  It  is  not 
infrequent  that  two  single  phase  meters  are  used  to 
measure  the  power  being  supplied  to  polyphase  in- 
duction motors ;  the  power  factor  of  an  induction 
motor  when  running  lightly  loaded  is  often  below 


/*  I  fie  Meter  Properly  Leveled fastened  to  Wall 

Is  the  Wall  f  Stone Wood 

or  Partition  \  Brick Cement 

f  Dampnett ribration 

Does  Location  of  Meter 

J  Chemical  Fumes Damage 

\Dust External  Magnetic  Fields 

W  IKING: 

Old  or  New 

Are  House  and  Service  Wires  in  Proper  Meter  Terminals _ 

Permit  Illegal  Use  of  Current 

(Evidence  of  S.  C.  on  Meter  Cover.) 

Start*  on folarity 

Creeping 

Sate Sev if  in See. 

Meter  Left 

Inspector's  Report 


50  per  cent,  in  which  case  one  of  the  two  single 
phase  meters  will  run  backward  when  properly  con- 
nected ;  care  should  therefore  be  taken  to  see  that  the 
meters  are  so  connected  that  both  of  them  will  run 
forward,  when  the  motor  is  operating  at  or  near  full 
load. 

The  card  shown  in  Fig.  86,  illustrates  the  form 
of  "Inspector's  Report"  as  used  by  the  Pacific  Gas 
&  Electric  Co.,  of  San  Francisco,  Cal.,  the  practice 
of  having  a  report  made  out  like  this  for  all  new 
installations  is  to  be  highly  recommended. 


MAINTENANCE  AND  TESTING  117 

Testing  and  Adjusting. 

To  insure  the  continued  accuracy  of  any  watt 
hour  meter  it  is  necessary  that  it  be  tested  and  ad- 
justed from  time  to  time.  In  the  smaller  meters 
it  is  not  necessary  to  make  these  tests  oftener 
than  about  once  a  year,  except  in  cases  of  complaint, 
and  when  meters  are  operating  under  adverse  condi- 
tions ;  in  the  larger  sizes,  where  a  small  variation  in 
accuracy  represents  a  considerable  amount  of  money, 
the  tests  should  of  course  be  made  oftener,  especially 
where  a  meter  of  large  capacity  is  called  upon  to 
register  a  small  percentage  of  its  rated  load  for  a  great 
part  of  the  time.  As  a  rule,  the  conditions  under 
which  the  meter  operates  will  dictate  in  a  large  meas- 
ure the  frequency  of  the  tests. 

The  experience  of  the  large  number  of  distribut- 
ing companies  that  have  adopted  some  method  of 
systematically  testing  and  adjusting  their  meters  has 
proven  that  the  increased  revenue  resulting  from 
more  accurate  meters  has  much  more  than  offset  the 
additional  expense  to  which  they  have  been  put,  be- 
sides reducing  trouble  and  complaints  due  to  occa- 
sional fast  meters. 

In  testing  meters  which  are  in  service  it  is  much 
better  to  test  and  make  any  necessary  adjustments  at 
the  point  of  installation,  rather  than  to  bring  the 
meter  into  the  testing  room,  since  with  the  proper 
instruments  the  same  accuracy  can  be  obtained  and 
a  great  saving  in  time  can  be  effected.  Such  practice 
also  avoids  those  injuries  to  the  meter  which  are  liable 
to  occur  in  transportation  to  and  from  the  customer's 
premises.  Of  course,  where  it  is  necessary  to  make 
repairs,  it  is  best  to  bring  the  meter  to  the  shop. 
That  particular  part  of  the  meter  which  usually  gives 
the  most  trouble  and  which  requires  the  most  fre- 
quent renewal  is  the  jewel  bearing.  Jewels  and  pivots 
can  be  renewed  at  the  point  of  installation  without 
disturbing  the  meter.  Friction  in  the  jewel  bearing 
will  result  in  the  meter  running  slow,  and  a  new 
jewel  should  be  substituted  whenever  a  defective  one 


118 


THE   WATTHOUR    METER 


is  located.  When  installing  a  new  jewel,  a  new  pivot 
or  ball  should  also  be  installed,  as  the  old  one  is  more 
than  apt  to  have  minute  particles  of  the  defective 
jewel  imbedded  in  it,  which  will  constitute  an  effective 
cutting  tool  and  will  soon  ruin  a  new  jewel.  In  the 
case  of  meters  employing  the  ball  and  jewel  bearing 
it  is  best  to  handle  the  ball  with  a  pair  of  tweezers 
rather  than  with  the  fingers,  as  the  moisture  from 
the  hands  may  cause  the  ball  to  rust. 

There  are  several  accurate  methods  used  for  test- 
ing watt  hour  meters,  and  the  choice  of  the  method  or 
methods  to  be  used  is  usually  determined  by  the  rela- 
tive convenience  of  that  method:  the  most  common 
are  (i)  the  voltmeter  and  ammeter  method,  (2)  the 
indicating  wattmeter  method  and  (3)  the  portable  ro- 
tating standard  method. 

Testing  with  Indicating  Instruments. 

The  voltmeter  and  ammeter  method  can  only  be 
used  with  direct  current  watt  hour  meters,  or  with 
alternating  current  watt  hour  meters  when  the  power 
factor  is  unity  or  its  exact  value  known ;  the  connec- 
tions for  this  method  are  shown  in  Fig.  87,  where  V 


Fig.  87. 


is  the  voltmeter,  A  is  the  ammeter  and  W  the  single 
phase  watthour  meter  being  tested.  If  E  is  the 
voltage  impressed  upon  the  circuit,  and  I  the  current 
in  amperes,  then  the  power  (unity  power  factor)  is 
P=E  x  I. 

The  indicating  wattmeter  method  of  testing  watt 


MAINTENANCE  AND  TESTING 


119 


hour  meters  is  applicable  to  alternating  currents  re- 
gardless of  what  the  power  factor  may  be,  so  with 
this  method  the  power,  P,  is  read  direct.  Fig.  88 
shows  the  connections  for  this  method  of  testing. 

Each  revolution  of  the  meter  disc  represents  a 
certain  number  of  watt  hours  of  electrical  energy  pass- 
ing through  the  meter,  which  is  given  in  some  types 
of  meters  directly  in  the  form  of  the  meter  "con- 
stant," and  in  such  meters,  if  R  is  the  number  of  revo- 
lutions of  the  disc  in  t  seconds  (as  measured  with  a 
stop  watch),  and  with  constant  power  passing  through 


Fig. 


the  meter,  then  the  watt  hours  would  be  =R  x  Ky 
where  K  is  the  meter  "constant."  But  the  power 
P=watt  seconds  per  second=watt  hours  x  3,600  di- 
vided by  the  time,  t,  therefore  we  have 

p  =  R  K  3,600 

The  constant,  K,  for  the  General  Electric  meters  will 
be  found  marked  on  the  meter  disc,  and  are  also  re- 
produced in  the  accompanying  tables. 


120 


THE    WATTHOUR    METER 


DIRECT  CURRENT  METERS. 


100-120  Volt 
Type  CH> 

1 

200-240  Volt. 
2  and  3  wire. 
Type  C-6 

s 

500-600  Volt 
Type  C-7 

a 
E 

O, 

IH 

.  0 

be'z: 
o  ec 

to 

a:  C 

Qu 

|E 

IH 

ll     ll 

£E 

Is 

l~* 

.  O 
5J  "S 

w 

S3 

.2  —' 

I! 

5 

2 

500 

none 

12 

.4 

250       none 

24 

1 

100 

none 

60 

10 

.4 

250 

24 

.75 

133.33     " 

45 

2 

50 

120 

15 

.6 

166.66 

36 

1.25 

80 

75 

3 

33.33 

180 

25 

1.0 

100 

60 

2.00 

50 

120 

5 

20 

300 

50 

2.0 

50 

120 

4.00 

25 

240 

10 

10 

" 

600 

75 

3.0 

33.33 

•• 

180 

6.00 

16.66     " 

360 

15 

66.66 

10 

900 

100 

4.0 

25 

240 

7.50 

13.33     •' 

450 

20 

50 

10 

1200 

150 

6,0 

16.66 

360 

12.50 

80         10 

750 

30 

33.33 

10 

1800 

300 

12.5 

80 

10 

750 

25.00 

40         10 

1500 

60 

16.66 

10 

3600 

600 

25.0 

40 

10 

1500 

*50.00 

*20         10 

300 

125 

80 

100 

7500 

*Applies  to  600  amperes,  two  wire  meters  only:  600  ampere,  three  wire  meters 
are  not  manufactured. 


General  Electric,  Type  "I,"  Standard  60  Cycle,  Single  Phase 
Watthour  Meters. 


100-130  Volt 
2  Wire 

200-260  Volt 
2  and  3  WTire 

500-600  Volt 

Amps 

Meter 
"K" 

Watts 
per  r.p.m. 

Meter         Watts 
"K"       per  r.p.m. 

Meter 
"K" 

Watts 
•per  r.p.m. 

3 

2 

12 

. 

4 

24 

1 

60 

5 

.3 

18 

6 

36 

1.5 

75 

10 

.6 

36 

1. 

25 

75 

3 

180 

15 

1 

60 

2 

120 

5 

300 

25 

1 

.5 

90 

3 

180 

7.5 

450 

50 

3 

180 

6 

360 

15 

900 

75 

5 

300 

10 

600 

25 

1500 

100 

6 

360 

12. 

5 

750 

30 

1800 

150 

10 

600 

20 

1200 

50 

3000 

200 

12 

.5 

750 

25 

1500 

60 

3600 

300 

20 

1200 

40 

2400 

100 

6000 

Polyphase, 

60 

Type 

"D-3." 

3 

.4 

24 

75 

45 

2     ' 

120 

5 

.6 

36 

1. 

25 

75 

3 

180 

10 

1. 

,25 

75 

2. 

5 

150 

6 

360 

15 

2 

120 

4 

240 

10 

600 

25 

3 

180 

6 

360 

15 

900 

50 

6 

360 

12. 

5 

750 

30 

1800 

75 

7 

.5 

450 

15 

900 

40 

2400 

100 

12, 

,5 

750 

25 

1500 

60 

3600 

150 

15 

900 

30 

1800 

75 

4500 

For  General  Electric  meters  used  with  current 
and  potential  transformers,  but  calibrated  without 
them,  the  constant  to  be  used  is  that  marked  on  the 
meter  disc,  divided  by  the  product  of  the  ratios  of  the 
potential  and  current  transformers.  The  worm  reduc- 
tion in  all  General  Electric  meters  is  100  and  will  be 


MAINTENANCE  AND  TESTING  121 

found  stamped  on  the  back  of  the  register.  The  regis- 
ter ratio  multiplied  by  ioo=number  of  revolutions  of 
disc  for  one  revolution  of  the  right  hand  pointer.  In 
all  cases,  the  meter,  K,  is  the  actual  number  of  watt 
hours  per  revolution  of  the  disc. 

*Rating  in   (volt-amperes) 
Meter  Constant,  K= 

Full  load  r.p.m.  of  disc  x  60 

0  -p,     .          Watt  hours  of  right  hand  dial 

Register  Ratio=    -   — —  — — - 

Worm   reduction   x   K 

(*For  polyphase  meters,  the  rating  should  be  multiplied 
by  2.  In  case  a  meter  has  a  double  rating,  such  as  110/220 
volts,  the  latter  voltage  should  be  applied  in  the  formula.  The 
approximate  full  load  speed  of  all  G.  E.  type  "I"  and  "D-3,"  60 
cycle  meters  is  30  r.p.m.) 

Westinghouse  Meter  Constants. 

For  different  makes  of  meters,  the  testing  for- 
mula given  takes  a  different  form  since  the  constant 
K  is  made  to  embrace  different  factors. 

For  the  Westinghouse  meter,  the  formula  be- 
comes 

P_RXK 

t 

where  K  represents  the  watt-seconds  for  one  revolution 
of  the  meter  disc. 

The  values  of  the  constant,  K,  for  the  Westing- 
house  types  B  and  C  and  for  the  direct  current  meters 
are  as  follows : 

2-wire  D.  C.  and  self-contained  single  phase,  K  =  volts  x  amps  x 

2.4; 
2-wire   single   phase   used   with   current  transformers    only    (but 

checked  without),  K  =  volts  x  5  x  2\4; 
2-wire,  single  phase  used  with  current  and  potential  transformers 

(but  checked  without),  K  =  5x100x2.4; 
2-wire,   single  phase,   used  with  transformers  of  either  or  both 

forms   (and  checked  with),  K  —  volts  x  amps  x  2.4; 
3-wire,  single  phase,  self-contained,  K  =  volts  x  amps,  x  4.8. 
3-wire,  single  phase,  used  with  current  transformers   (but  checked 

wtihout),  Revolts  (as  marked  on  meter)  x  12; 
Type  "C"  polyphase,  self-contained,  K  =  volts  x  amps  x  4.8 ; 
Type  "C"  polyphase,  used  with  current  transformers  only  (but 

checked  without),  K  =  5  x  volts  x4.8; 


122  THE   WATTHOUR    METER 

Type  "C"  polyphase,  used  with  current  and  potential  transformers 

(but  checked  without),  K  =  2400; 
Type   "C"  polyphase   used  with  transformers   of  either  or   both 

forms  (and  checked  with),  K^  volts  x  amps  x  4.8. 
In  all  cases,  the  volt  and  ampere  values  referred 
to  are  those  as  marked  on  the  name  plate  of  the 
meter.  The  full  load  speed  of  the  types  B  and  C  is 
25  r.p.m.  For  the  Westinghouse  type  A  meter,  the 
full  load  speed  is  50  r.p.m.,  and  the  constant,  K,  for 
this  type  is  exactly  one-half  the  value  of  a  similarly 
rated  type  C  meter. 

Fort   Wayne   Type    K   Meter. 

The  calibrating  equation  of  the  Fort  Wayne  type 
K  meter  is  as  follows  : 

p_RXK  X  100 

t 

where  t  is  the  time  in  seconds  during  which  the  meter 
makes  R  revolutions,  and  where  K  is  the  constant, 
which  will  be  found  in  the  following  tables  : 

Fort  Wayne,  Type  "K,"  Single  Phase,  60  Cycle  Watthour  Meters 

whose  Serial  Number  is  344,999  or  less. 

Values  of  the  Constant,  K. 


a 

£o 

<y  O 

.«  > 

2  > 

2  ° 

£.  ° 

O  >. 

2  > 

E 

^  > 

°£o 

'io 

'^Q 

'58 

'58 

< 

eg  5? 

rg^H 

<N  CM 

rocvi 

CXJU} 

CM^ 

CN  CM 

3 

9 

18 

18 

45 

90 

90 

5 

9 

9 

18 

18 

45 

90 

180 

7.5 

27 

10 

9 

18 

36 

36 

90 

180 

360 

15 

18 

36 

54 

54 

180 

360 

540 

20 

18 

36 

72 

72 

180 

360 

720 

25 

18 

36 

72 

72 

180 

360 

900 

30 

36 

72 

90 

90 

360 

720 

1080 

40 

36 

72 

108 

108 

360 

720 

1440 

50 

36 

72 

144 

144 

360 

720 

1800 

60 

54 

108 

180 

180 

540 

1080 

2160 

75 

54 

108 

216 

216 

540 

1080 

2700 

100 

72 

144 

288 

288 

720 

1440 

3600 

125 

90 

180 

360 

360 

900 

1800 

4500 

150 

108 

216 

432 

432 

1080 

2160 

5400 

200 

144 

288 

576 

576 

1440 

2880 

7200 

250 

180 

360 

720 

720 

1800 

3600 

9000 

300 

270 

540 

1080 

1080 

2700 

5400 

10800 

400 

360 

720 

1440 

1440 

3600 

7200 

14400 

500 

450 

900 

1800 

1800 

4500 

9000 

18000 

600 

540 

1080 

2160 

2160 

5400 

10800 

21600 

800 

720 

1440 

2880 

2880 

7200 

14400 

28800 

1000 

900 

1800 

3600 

3600 

9000 

18000 

36000 

Use  These  Constants  for  High  Torque  Meters. 
15  13.5  27  54  54  135  270  540 

30  27.0  54  90  96  270  540  1080 


MAINTENANCE  AND  TESTING 


123 


Fort  Wayne,  Type  "K,"  Single  Phase,  60  Cycle  Watthour  Meters, 

whose  Serial  Number  is  345,000  or  above. 

Values  of  the  Constant,  K. 


in 

v~o 

0*0 

<u~o 

G"O 

jB*O 

£>£ 

fi? 

E 

'io 

£o 

'io 

£Q 

£0 

"S§ 

'i8 

< 

CN-^H 

CN<SI 

roRi 

rvi5 

CM  1/5 

CM-i-l 

<M£! 

5 

9 

18 

18 

36 

45 

90 

180 

10 

18 

36 

3  6 

72 

90 

180 

360 

15 

27 

54 

54 

108 

135 

270 

540 

20 

36 

72 

72 

144 

180 

360 

720 

25 

45 

90 

90 

180 

225 

450 

900 

40 

72 

144 

144 

288 

360 

720 

1440 

50 

90 

180 

180 

360 

450 

900 

1800 

75 

135 

270 

270 

540 

675 

1350 

2700 

100 

180 

360 

SCO  • 

720 

900 

1800 

3600 

125 

225 

450 

450 

900 

1125 

2250 

4500 

150 

270 

540 

540 

1080 

1350 

2700 

5400 

200 

360 

720 

720 

1440 

1800 

3600 

7200 

300 

540 

1080 

1080 

2160 

2700 

5400 

10800 

400 

720 

1440 

1440 

2880 

3600 

7200 

14400 

600 

1080 

2160 

2r60 

4320 

5400 

10800 

21600 

800 

1440 

2880 

2880 

5760 

7200 

14400 

28800 

Fort  Wayne,  Type  "K,"  Polyphase  Meters  whose  Serial  Number 

is  344,999  or  less. 
Values  of  the  Constant  K. 


Amps. 

110  v. 

220  v. 

440  v. 

550  v. 

1100  v. 

2200  v. 

3 

18 

36 

72 

90 

180 

360 

5 

36 

72 

144 

180 

360 

720 

10 

72 

144 

288 

360 

720 

1440 

15 

108 

216 

432 

540 

1080 

2160 

20 

144 

288 

576 

720 

1440 

2880 

25 

144 

288 

576 

720 

1800 

3600 

30 

216 

360 

720 

1080 

2160 

4320 

40 

288 

576 

1152 

1440 

2880 

5760 

50 

288 

576 

1152 

1440 

3600 

7200 

60 

432 

864 

1728 

2160 

4320 

8640 

75 

432 

864 

1728 

2160 

5400 

10800 

100 

576 

1152 

2304 

2880 

7200 

14400 

125 

720 

1440 

2880 

3600 

9000 

18000 

150 

864 

1800 

3600 

4320 

10800 

21600 

200 

1440 

2880 

5760 

7200 

14400 

28800 

250 

1800 

3600 

7200 

9000 

18000 

36000 

300 

2160 

4320 

8640 

10800 

21600 

43200 

400 

2880 

5760 

11520 

14400 

28800 

57600 

500  . 

3600 

7200 

14400 

18000 

36000 

72000 

600 

4320 

8640 

17280 

21600 

43200 

86400 

800 

5760 

11520 

23040 

28800 

57600 

115200 

1000 

7200 

14400 

28800 

36000 

72000 

144000 

124 


THE    WATTHOUR    METER 


Fort  Wayne,  Type  "K"  Polyphase  Meters  whose  Serial  Number 

is  345,000  or  above. 
Values  of  the  Constant,  K. 


Amps. 

5 

10 
15 
25 
50 
75 

100 

150 

200 

300 

400 

600 

800 


110  v. 

36 

72 

108 

180 

360 

540 

720 

1080 

1440 

2160 

2880 

4320 

5760 


220  v. 

72 

144 

216 

360 

720 

1080 

1440 

2160 

2880 

4320 

5760 

8640 

11520 


440  v. 

144 

288 

432 

720 

1440 

2160 

2880 

4320 

5760 

8640 

11520 

17280 

23040 


550  v. 

180 

360 

540 

900 

1800 

2700 

3600 

5400 

7200 

10800 

14400 

21600 

28800 


1100  v. 

2200  v. 

360 

720 

720 

1440 

1080 

2160 

1800 

3600 

3600 

7200 

5400 

10800 

7200 

14400 

10800 

21600 

14400 

28800 

21600 

43200 

28800 

57600 

43200 

86400 

57600 

115200 

The  Duncan  Meter. 

The  formula  for  testing  meters  manufactured  by 
the     Duncan     Electric     Manufacturing    Company    is 
F_RXKX3600 

which  is  the  same  as  that  previously  given  for  the 
General  Electric  meter.  The  following  is  a  table  of 
testing  constants : 

110  Volts  220  Volts  550  Volts 


Amps. 

Meter 
"K" 

Watts 
per  r.p.m. 

2.5 

0.25 

15 

5 

0.25 

15 

7.5 

0.50 

30 

10 

0.50 

30 

15 

1 

60 

25 

1 

60 

50 

2 

120 

75 

3 

180 

100 

4 

240 

150 

6 

360 

200 

8 

480 

300 

12 

720 

450 

20 

1200 

600 

25 

1500 

800 


30 


1800 


Meter 

Watts 

"K" 

per  r.p.m. 

0.5 

30 

0.5 

30 

1 

60 

1 

60 

2 

120 

2 

120 

4 

240 

6 

360 

8 

480 

12 

720 

16 

960 

25 

1500 

30 

1800 

50 

3000 

60 

3600 

Meter 

Watts 

"K" 

per  r.p.m. 

1 

60 

1 

60 

2 

120 

2 

120 

5 

300 

5 

300 

10 

600 

16 

960 

20 

1200 

30 

1800 

40 

2400 

60 

3600 

80 

4800 

100 

6000 

160 

9600 

Sometimes    it    is    necessary    to    use  the    formula 

already  given   for  the   determination  of  other  values 

than  the  watts,  P,  and  for  convenience  this   formula 
is  rewritten  as   follows : 


(1)    Number  of  revolutions  = 


_  Sees,  during  test  x  watts  indicated 
3600  x  testing  constant  (K) 

seconds  during  test  x  watts  indicated 
(2)    Testing  constant  =  -  ^      *  — = — 

3600  x  revolutions. 

3600  x  revolutions  x   testing  constant 


(3)    Seconds  = 


watts  indicated 


MAINTENANCE  AND  TESTING  125- 

The  Sangamo  Mercury  Meter. 

A  description  of  the  Sangamo  Mercury  Meter 
will  be  found  in  Chapter  V.,  the  table  of  calibrating 
constants  being  given  below  : 

Amps.  100/125  volts.          200/250  volts.  500/600  volts. 

5  A.  C.  1,800  3,600  ........ 

5  D.  C.  2,400  4,800  12,000 

10  2,400  4,800  12,000 

20  4.800  9,600  24,000 

30  7,200  14,400  36,000 

40  9,600  19,200  48,000 

60  14,400  28,800  72,000 

80  19,200  38,400  96,000 

100  24,000  48,000  120,000 

150  36,000  72,000  180,000 

200  48,000  96,000  240,000 

300  72,000  144,000  360,000 

400  96,000  192,000  480,000 

500  120,000  240,000  600,000 

600  144,000  288,000  720,000 

800  192,000  384,000  960,000 

1000  240,000  480,000  1,200,000 

The  calibrating  equation  for  the  Sangamo  is  the  same 
as  for  the  Westinghouse  meter,  viz.  : 


t    ' 

in  which  the  constant,  K  =  watt-seconds  recorded  by 
one  revolution  of  the  disc. 

Larger  capacity  meters  than  given  in  the  above 
table  have  proportionally  greater  values  of  K. 

Three  wire  110-220  volts  A.  C.  meters  have  same 
constants  as  above  given  for  the  200-250  volt  meters. 

Testing  with  the  Portable  Rotating  Standard. 

The  third  method  of  testing  watthour  meters,  and 
probably  the  most  convenient  and  the  quickest  for 
outside  work,  consists  in  using  a  portable  standard 
watt  hour  meter,  which  is  usually  known  as  a  "rotating 
standard."  It  is  especially  well  adapted  for  the  rapid 
testing  of  service  meters  at  the  point  of  installation. 
The  portable  standard  eliminates  the  necessity  of  a 
stop  watch,  since  the  time  element  does  not  enter  into 
account  ;  furthermore,  the  load  does  not  have  to  remain 
constant  during  the  test,  as  is  the  case  with  both  of 
the  previously  named  methods;  the  only  thing  which 


126 


THE    WATTHOUR    METER 


has  to  be  observed  is  the  number  of  revolutions  of  the 
disc  of  the  meter  under  test ;  the  disc  of  the  rotating 
standard  is  directly  connected  to  the  large  or  lowest 
reading  pointer,  and  therefore  indicates  the  actual  num- 
ber of  revolutions  which  it  makes.  Figure  89  shows 
interior  and  exterior  view  of  a  typical  type  of  rotat- 
ing standard  test  meter.  This  type  of  meter  is  essen- 
tially an  ordinary  watthour  meter  with  certain  modi- 
fications. It  is  made  with  several  different  current  coils 
whose  leads  are  brought  out  to  a  connection  block 
on  the  top  of  the  meter  or  to  a  drum  switch  within, 
and  that  coil  whose  capacity  is  nearest  the  value  at 
which  the  meter  under  test  is  operating  can  be  con- 
nected in  the  circuit.  By  this  means  the  test  meter 


Fig.  89. 

can  always  be  made  to  operate  at  or  near  full  load, 
therefore  having  its  full  load  accuracy  throughout  a 
wide  range.  This  is  an  excellent  feature,  as  it  insures 
accuracy  over  a  wide  range  and  also  permits  the  use 
of  one  test  meter  for  calibrating  watthour  meters  of 
various  sizes. 

The  rotating  standard  is  made  self-contained  in 
the  following  sizes:  Direct  current,  110-220  volts,  with 
current  coils  for  I,  2,  10,  20  and  40  amperes,  or  with 
current  coils  for  5,  10,  50  and  100  amperes ;  alternating 
current,  110-220  volts,  with  current  coils  for  i,  10  and 
20  amperes,  or  with  current  coils  for  I,  5,  10,  50  and 
loo  amperes.  By  means  of  "multipliers"  or  potential 
transformers,  these  instruments  can  be  used  on  440 
and  550  volts. 

The  rotating  standard  is  very  carefully  designed 


MAINTENANCE  AND  TESTING  127 

and  is  well  built  mechanically.  The  registering  mechan- 
ism is  simple,  since,  as  previously  stated,  the  disc  shaft 
is  directly  connected  to  the  lowest  reading  pointer. 
The  complete  dial  is  usually  made  up  of  two  pointers, 
the  ratio  being  such  that  the  highest  reading  pointer 
will  not  repeat  its  reading  within  less  time  than  about 
two  and  one-half  minutes  when  operating  at  full  load 
speed.  The  number  of  revolutions  of  the  disc  as  in- 
dicated by  the  pointers,  multiplied  by  the  constant  for 
the  particular  coil  of  the  standard  which  is  connected 
in  circuit,  gives  the  watt  hours  that  have  passed  during 
the  time  it  is  connected  to  the  circuit,  or 

P  =  RxK   (Gen.  Elec.  Rotating  Standard). 
The  accuracy  of  the  meter  under  test  is  expressed  by 
the   following   equation  : 

r  x  k 

Percentage  of  accuracy  -  -=  x  100,  where 

K.  x  iv 

r=revolutions  of  disc  of  meter  under  test  ; 

k=constant   of   meter   under   test; 

R=revolutions   of  rotating  standard   as   indicated   by 

register  ; 

K,=constant  of  coil  being  used  in  standard. 

For  General  Electric  meters,  k  is  marked  on  the 
disc. 

c   x   watt    rating 
ror  Westinghouse   meters,  k  =  — 


where  c  is  the  value  of  the  constant  for  Westinghouse 
meters: 

For  Fort  Wayne  meters,  k  =  T^-,     where    "c"     is 

the  value  of  the  constant  as  given   for  Fort  Wayne 
meters. 

In  the  case  of  the  rotating  standard,  the  value 
of  the  constant  K  for  the  individual  coils  is  the  same 
as  in  the  standard  service  meters.  For  instance,  the 
value  of  K  for  the  lo-ampere  coil  in  the  rotating 
standard  is  the  same  as  the  constant  for  a  lo-ampere 
service  meter,  so  that  when  testing  service  meters  with 
a  rotating  standard  and  at  the  same  time  using  the 
coil  of  the  standard  meter  which  is  of  the  same  capac- 


128 


THE   WATTHOUR    METER 


ity  as  the  meter  under  test,  is  is  only  necessary  to 
compare  the  revolutions  of  the  two  meters,  that  is : 

Percentage  of  accuracy  =  -=-  x  100,  or  the 

K 

Percentage  of  error  =  -  x  100,  where 

K. 

r==revolutions  of  the  meter  under  test,  and  R=  revo- 
lutions of  standard. 

Below  is  given  a  table  of  data  to  be  used  with 
the  Westinghouse  rotating  standard  .when  used  in 
checking  induction  meters  manufactured  by  the  West- 
inghouse  Company,  the  General  Electric  Company  and 
the  P'ort  Wayne  Electric  Works : 


S'dMrf 

fitter 


fo  tv  /o6% 


oS  Series 


KS.SI  KSJif  ;eX 


>f^;  &?.o4 


3/.9J  J/JB  3tZ5  30.-)S30.t 


/y/s  /f.9f 
/.xt  / 


/.xx 


XfT*  Jtf-ftt  Xf./3 


X7.F4- 


X7.X 


K.o 


/.9X 


/•90 


/.et 


/.ft 


33.4*  SJ.tf  Zt 


ZS.3SZS.6t  Z3.&  X3.Z4>Z*&  XX.73  ZX-&  ZXAt X*.<X>  ?/  ft  Z./43 


/-ft 


JSo 

X..O     *0 


/.ff  /.f6  /.jy  /.S3  /.fx  /  f<y  /jf 


Fig.  90 


MAINTENANCE  AND  TESTING 


129 


The  constant  of  any  coil  of  the  Westinghouse 
rotating  standard  is  the  same  as  the  constant  of  a 
Westinghouse  service  meter  having  the  same  ampere 
capacity  as  that  coil,  so  that  the  meter  under  test 
and  the  standard  should  make  the  same  number  of 
revolutions  if  the  meter  under  test  is  correct. 

The  general  connections  of  the  test  meter  are 
shown  in  Figure  91.  After  the  connections  have  all 
been  made  the  meter  is  started  and  stopped  by  simply 
closing  or  opening  the  little  push  button  switch,  S. 
The  meter  tester  has  only  to  close  the  potential  circuit 
by  means  of  this  switch,  note  the  number  of  revolu- 
tions made  by  the  standard  and  by  the  meter  under 
test  and  apply  these  values  in  the  above  formula,  from 


Sow 


600 
o   o    o 


'Fig.  91. 


which  he  can  immediately  obtain  the  percentage  ac- 
curacy of  the  meter  under  test.  If  it  is  found  to  be 
too  fast  or  too  slow  it  should  be  adjusted  as  previously 
explained.  Meters  should  be  adjusted  for  accuracy 
both  on  full  load  and  about  5  per  cent  load,  and  it 
should  be  within  2  per  cent  correct  throughout  this 
range. 

In  using  a  portable  rotating  standard  it  should 
be  remembered  that  it  must  be  calibrated  from  time 
to  time  by  checking  it  against  laboratory  standards. 

When  testing  meters  at  the  point  of  installation 
it  is  usually  more  convenient  to  have  some  kind  of 
a  "portable  load,"  which  will  consist  of  a  lamp  bank 
or  other  resistance  suitably  mounted  so  that  it  may  be 
carried  from  place  to  place,  rather  than  to  use  the 


130 


THE   WATTHOUR   METER 


customer's  load  for  testing  purposes.  With  the  "port- 
able load"  the  tester  can  do  his  work  quicker  and  he 
can  get  the  exact  load  which  he  desires  to  put  on  the 
meter  under  test. 

Phantom  Loads. 

A  method  of  testing  watthour  meters  under  full 
load  conditions  with  a  small  consumption  of  power  is 
to  connect  the  potential  circuit  of  the  meter  in  the 
usual  way  and  connect  the  current  coils  in  series  with 


Fig.  92. 

the  secondary  of  a  small  transformer  especially  de- 
signed for  this  purpose,  the  primary  of  the  transformer 
being  connected  in  parallel  with  the  line  as  shown  in 
Fig.  92,  thus  having  the  same  potential  impressed  upon 
it  as  upon  the  potential  coil  of  the  meter.  The  resist- 
ance (R)  is  connected  in  series  with  the  secondary 
windings,  so  that  portions  of  it  can  be  short  circuited 
by  means  of  suitable  plugs  or  switches  in  order  that 
the  desired  current  may  be  obtained.  If  the  trans- 


MAINTENANCE  AXD  TESTING  131 

former  is  properly  designed  and  the  connections  prop- 
erly made,  the  secondary  current  flowing  through  the 
current  coils  of  the  meter  will  be  approximately  in 
phase  with  the  impressed  e.m.f.  Full  load  current  or  de- 
sirable portions  of  full  load  current  can  be  obtained  for 
the  meter  under  test,  while  the  primary  circuit  takes 
only  a  very  small  amount  of  current  from  the  line. 
This  method  of  testing  is  especially  convenient  in  test- 
ing meters  on  high  potential  circuits,  as  the  potential 
transformers  ordinarily  used  can  also  be  made  to  sup- 
ply the  current  for  testing  purposes  through  the  agency 
of  this  "phantom  load  transformer."  Such  a  trans- 
former is  usually  designed  to  take  about  one-half  am- 
pere at  no  volts,  while  supplying  5  amperes  to  the 
meter  under  test. 


Fig,  93. 

The  "phantom  load  transformer"  is  small  and  com- 
pact and  can  be  easily  carried  from  place  to  place ; 
in  connection  with  the  portable  rotating  standard  it 
furnishes  a  very  complete  set  for  testing  the  average 
size  service  meter.  This  transformer  can  be  very  ad- 
vantageously used  for  testing  meters  on  50  per  cent 
power  factor  where  three-phase  current  is  available, 
which  is  always  the  case  where  this  adjustment  is 
most  important,  namely  on  three-phase  power  circuits. 
Let  Figure  93  represent  the  vector  diagram  of  the  volt- 
ages in  a  three-phase  system ;  then  if  the  voltage  AC 
is  impressed  upon  the  potential  winding  of  the  meter, 
and  the  primary  of  the  phantom  load  transformer  is 


132  THE   WATTHOUR    METER 

connected  across  BA  or  BC,  the  current  flowing  in 
the  secondary  of  the  transformer,  and  therefore 
through  the  meter  windings,  will  be  60  degrees  out  of 
phase  with  the  voltage  AC,  or  in  other  words,  we  \vill 
have  a  power  factor  of  50  per  cent.  One  of  the  con- 
nections referred  to  will  give  a  50  per  cent  leading 
power  factor  and  the  other  will  give  a  50  per  cent 
lagging  power  factor,  but  it  is  better  to  make  any 
necessary  adjustments  on  lagging  power  factor,  as 
the  meter  usually  operates  under  this  condition. 

To  distinguish  between  the  connection  for  lead- 
ing power  and  lagging  power  factor,  most  of  the  re- 
sistance in  the  secondary  circuit  of  the  phantom  load 
transformer  is  short  circuited  and  a  reactance  cut  into 
the  circuit.  This  reactance  causes  the  current  in  the 
secondary  to  lag  behind  the  secondary  e.m.f.,  and 
when  the  primary  of  the  transformer  is  connected 
across  the  proper  lines  to  give  a  lagging  power  factor 
in  the  meter  under  test,  the  current  will  lag  more  than 
60  degrees,  and  the  power  factor  will  therefore  be  less 
than  50  per  cent,  while  if  connected  to  the  proper  lines 
for  leading  power  factor  the  current  will  lag  less  than 
60  degrees  and  the  power  factor  will  therefore  be  more 
than  50  per  cent,  thereby  causing  the  meter  to  run 
slower  when  the  transformer  is  connected  across  the 
proper  lines  for  lagging  power  factor;  as  soon  as  this 
is  determined  the  reactance  is  switched  out,  the  power 
factor  then  being  approximately  50  per  cent  lagging, 
after  which  the  test  may  be  continued. 

The  Knopp  Method  of  Meter  Testing. 

A  method  in  use  by  the  Pacific  Gas  &  Electric  Co., 
of  San  Francisco,  Cal.,  for  testing  watthour  meters, 
and  known  as  the  "Knopp  method"  is  as  follows : 

The  tester  is  provided  with  a  portable  resistance 
box  upon  which  is  mounted  an  indicating  ammeter, 
illustration  of  which  is  shown  in  Fig.  94  (a)  ;  he  is 
also  supplied  with  a  stop  watch  which  has  a  special 
dial  that  indicates  millihours  rather  than  seconds ;  the 
large  hand  (corresponding  to  the  second  hand  of  the 


MAINTENANCE  AXD  TESTING  133 

ordinary  stop  watch)  of  this  watch  makes  one  revolu- 
tion in  36  seconds,  the  dial  being  divided  into  100 
equal  parts,  each  division  representing  i-io  millihour. 
The  resistance  box  has  several  coils,  different  combina- 
tions of  which  are  used  for  different  loads,  each  coil  be- 
ing adjusted  to  consume  a  definite  amount  of  power  at 
a  predetermined  potential.  The  box  also  has  a  variable 
resistance  in  series  with  the  loading  resistance,  which 
can  be  varied  by  means  of  a  sliding  contact  provided 
for  that  purpose.  By  the  use  of  this  variable  resistance 


Fig.  94a. 

the  voltage  drop  across  it  may  be  made  equal  to  the 
difference  between  the  line  voltage  and  the  predeter- 
mined (TOO  volts)  voltage,  or  in  other  words,  so  that 
this  voltage  is  impressed  upon  the  load  resistance  re- 
gardless of  the  value  of  the  line  voltage,  which  condi- 
tion when  reached  will  be  indicated  by  the  ammeter; 
that  is,  for  any  coil  the  ammeter  will  indicate  a 
certain  definite  current.  The  potential  tap  for  the 
watthour  meter  is  connected  inside  of  the  resistance 
box  so  that  the  voltage  impressed  upon  the  meter  will 
be  the  same  as  that  impressed  upon  the  load  coils. 


134  THE    WATTHOUR    METER 

The  load  coils  of  the  portable  resistance  box  are 
adjusted  to  consume  such  an  amount  of  power  that 
the  meter  to  be  tested  will,  if  correct,  make  one,  ten  or 
twenty  revolutions  in  36  seconds,  or  during  one  com- 
plete revolution  of  the  hand  of  the  special  millihour 
watch.  All  that  the  meter  tester  has  to  do,  therefore, 
is  to  connect  in  the  box,  obtain  the  proper  current  (by 
means  of  the  various  resistances),  as  indicated  by  the 
ammeter,  and  then  note  the  time  with  the  special 
stop  watch  of  one,  ten  or  twenty  revolutions  of  the 
meter  disc,  depending  upon  which  load  the  meter  is 
being  tested.  From  the  reading  of  the  stop  watch  the 
accuracy  of  the  meter  can  be  obtained  directly  without 
the  use  of  a  formula.  If  the  watch  has  made  exactly 
one  revolution  (for  the  load  chosen),  the  meter  is 
correct,  while  if  the  hand  of  the  watch  lacks  two  divi- 
sions the  meter  is  approximately  2  per  cent  fast,  or  if 
the  hand  has  made  a  complete  revolution  and  two 
divisions  past,  the  meter  is  approximately  2  per  cent 
slow.  This  method  of  testing  service  watthour  meters 
is  convenient,  since  the  outfit  is  light  and  compact,  and 
it  is  also  very  quick. 

Figure  94  (b)  shows  the  diagram  of  connections 
of  the  "Knopp  set,"  the  name  being  derived  from  the 
patentee,  Mr.  Otto  A.  Knopp.  For  testing  no-volt 
meters,  the  plugs  o,  a,  b  and  c  are  used,  and  for  testing 
22O-volt  meters  the  plugs  o',  a',  b',  c'  and  d  are  used. 
An  example  of  the  method  of  using  this  set  is  as  fol- 
lows :  Suppose  that  it  is  desired  to  test  a  5-ampere, 
i  zo-volt  induction  watthour  meter  having  a  calibrating 
constant  of  .3.  The  box  is  connected  into  circuit  and 
a  resistance  is  plugged  in  to  give  600  watts  ;  the  vari- 
able resistance  is  adjusted  until  the  ammeter  indicates 
0.600  ampere  (i-io  of  the  current  passing  in  shunt 
through  the  ammeter).  The  time  for  20  revolutions  of 
the  disc  is  taken  with  the  millihour  watch ;  the  time 
taken  for  the  20  revolutions  should  be  the  same  as 
taken  for  one  revolution  of  the  hand  of  the  watch.  The 
percentage  error  will  be  indicated  by  the  watch,  as  has 
already  been  explained.  When  the  meter  has  been  ad- 


MAINTENANCE  AND  TESTING 


135 


justed  for  full  load  (600  watts  approximately),  another 
resistance  which  takes  30  watts  is  plugged  into  circuit 
and  the  600- watt  load  cut  out ;  the  variable  resistance 


1  1 

.U-.-J   .---I.. 

\ 

"%zr 

r 
/Qmmeter 

Fig.  94b. 

is  adjusted  until  the  ammeter  indicates  0.30  ampere; 
if  the  meter  is  correct  the  disc  will  make  one  revolution 
while  the  hand  of  the  millihour  watch  makes  one  revo- 
lution. 


136  THE   WATTHOUR   METER 

The  voltage  of  the  circuit  can  be  read  with  this 
outfit  by  switching  in  the  i-ampere  resistance  coil  and 
cutting  the  variable  resistance  entirely  out.  The  i- 
ampere  coil  has  a  resistance  of  100  ohms,  and  when  the 
line  voltage  is  impressed  upon  this  resistance  which  is 
in  series  with  the  ammeter  (which  is  1.5  amperes 
capacity),  the  voltage  of  the  circuit  can  be  read  directly 
from  the  ammeter.  Thus  if  the  line  voltage  is  100, 
the  ammeter  will  indicate  i.o  ampere  or  if  the  line 
voltage  is  no  the  ammeter  will  indicate  i.io  amperes, 
etc. 

By  referring  to  the  diagram  (Figure  94),  it  will 
be  seen  that  for  the  higher  loads  the  ammeter  is  con- 
nected in  shunt  with  the  resistances,  thereby  taking 
only  a  part  of  the  total  current.  By  employing  this 
method  of  connection,  the  ammeter  is  only  used  over 
the  most  accurate  part  of  the  scale  while  testing  watt 
hour  meters  of  different  sizes  and  at  different  loads. 

The  Knopp  millihour  watch  can  also  be  used  to 
advantage  when  testing  with  ordinary  indicating  in- 
struments, since  it  has  the  advantage  of  simplifying  the 
testing  formula  to  some  extent ;  the  formula 

R  x  K  x  3600   .  R  x  K  x  1000 

P  =  -        — ,  becomes  P  =  — ; —      ~, 

where  t'  is  the  time  is  millihours  as  read  with  the 
special  stop  watch. 

When  calibrating  meters  in  the  testing  room  with 
this  special  watch  the  load  can  be  adjusted  to  be  such 
a  multiple  of  the  disc  constant  that  the  disc  will  make 
one,  ten  or  twenty  revolutions  for  one  revolution  of 
the  hand  of  the  stop  watch  when  the  meter  is  correct. 
If  the  meter  is  not  correct,  the  percentage  inaccuracy 
will  be  indicated  by  the  watch.  Thus,  if  the  meter  is 
fast  the  watch  hand  will  not  quite  make  a  complete 
revolution,  while  if  the  meter  is  slow  the  hand  will 
make  more  than  a  complete  revolution. 

The  number  of  divisions  which  the  hand  lacks  of 
a  complete  revolution  is  the  percentage  by  which  the 
meter,  is  fast.  The  number  of  divisions  by  which  the 


MAINTENANCE  AND  TESTING  137 

hand  has  passed  a  complete  revolution  is  the  percent- 
age by  which  the  meter  is  slow. 

In  using  this  method  of  testing,  the  proper  load 
is  obtained  from  the  following  formula : 

RxKx  10000 
t' 

Pt'  =  =  R  x  K  x  10000;  for  one  revolution  of  the 
stop-watch  hand,  t'  =  100,  therefore 

100  P=R  x  K  x  10,000, 
or   P=R  x   K  x   100. 

For  a  5-ampere  meter  having  a  constant  of  K=.3, 
and  using  one  revolution  of  the  disc  for  light  load  test 
gives  P=3O  watts.  For  full  load  test  taking  R=2O, 
we  will  get  P=6oo  watts. 

Portable  Testing  Set  for  Direct  Current  Watt  Hour 
Meters. 

For  outside  testing  of  direct  current  meters  the 
set  as  shown  diagramatically  in  Figure  95,  will  be 
found  to  be  convenient ;  it  is  compact  and  light,  there- 
fore easy  for  the  tester  to  carry  from  place  to  place. 
The  current  is  furnished  for  the  smaller  sizes  of  meters 
(5,  10  and  15  amperes),  from  an  ordinary  dry  cell, 
and  for  larger  meters  from  the  improved  type  of 
Edison  storage  battery,  the  current  being  regulated  by 
the  plug  resistances.  The  potential  is  taken  from  the 
line  through  the  variable  resistance  which  is  regulated 
by  a  sliding  contact  block.  Potential  and  current  are 
supplied  alike  to  the  watthour  meter  under  test  and 
to  the  combination  volt-ampere  indicating  meter  showrr 
at  the  top  of  the  diagram.  For  convenience  of  testing, 
the  volt-ampere  meter  has  several  potential  and  current 
ranges.  The  volt-ampere  meter  also  indicates  watts, 
the  indication  being  shown  on  a  scale  directly  beneath 
the  intersection  of  the  volt  needle  and  the  ampere 
needle.  After  selecting  the  proper  current  'as  indi- 
cated by  the  combination  meter,  the  wattage  is  held 
constant  by  means  of  the  variable  potential  resistance. 


138 


THE   WATTHOUR    METER 


onnnnnnnnnrH 


/X/V'V'V'S/N/'N/V'N/V^^/X/V'N/N/N/ M ' 

- — D — - 

l/\^x/N/V'V'V'\^v^v''V^/V'\/N/N/V'\/V__. 


Waft/tour  Meter 
Fig.  95. 


MAINTENANCE  AND  TESTING  139 

Adjustments. 

In  any  type  of  meter  if  the  actual  value  of  P  (in 
above  formula)  is  greater  than  that  expressed  by  the 
calibrating  equation  the  meter  under  test  is  slow, 
and  if  this  value  is  less  the  meter  is  fast.  If  we  rep- 
resent the  power  as  registered  by  the  watthour  meter 
by  P',  and  the  true  power  as  indicated  by  the  standard 
by  P,  the  error  in  percentage  may  be  expressed  by  the 

p p' 

equation,  error  =     —5 —   ><  100.  In  calibrating  watthour 

meters  it  will  be  found  to  be  more  convenient  to  use 
the  term  "percentage  of  accuracy"  or  "correction 
factor''  rather  than  the  term  "percentage  error,"  since 
the  former  method  involves  less  work  in  making  the 
computations.  For  example : 

p' 

Percentage  of  accuracy  =:  —  X  100, 

p 

Correction  factor  ==  7,7 

If  the  percentage  of  accuracy  is  less  than  100  the  meter 
is  slow ;  if  it  is  greater  the  meter  is  fast.  If  the  cor- 
rection factor  is  less  than  i  the  meter  is  fast,  and  if  it 
is  more  than  I  the  meter  is  slow. 

If  the  watthour  meter  under  test  is  found  to  be 
inaccurate  at  or  near  full  load,  the  retarding  magnets 
should  be  adjusted  until  the  meter  registers  correctly. 
If  it  is  slow,  the  magnets  should  be  moved  in  toward 
the  center  of  the  disc,  which  operation  will  increase  the 
speed,  while  if  the  meter  is  fast  the  retarding  magnets 
should  be  moved  out  toward  the  periphery  of  the  disc. 

If  the  meter  under  test  is  found  to  be  slow  on 
light  loads,  undue  friction  should  be  looked  for  and 
eliminated,  and  the  light  load  adjustment  (as  pre- 
viously explained  for  various  kinds  of  meters)  reset. 
If  the  meter  is  fast  on  very  light  loads,  or  if  it 
"creeps,"  the  light  load  adjusting  device  is  very  prob- 
ably exerting  too  much  torque,  and  its  effect  should 
be  decreased  until  the  meter  is  within  2  per  cent  ac- 
curacy on  a  5  per  cent  load. 


140 


THE    WATTHOUR    METER 


Shop  Methods  of  Testing. 

A  very  convenient  and  flexible  laboratory  test- 
ing board  is  shown  diagrammatically  in  Fig.  96,  which 
can  be  used  for  testing  single  phase  watthour  meters 
of  voltages  from  100  to  500  inclusive,  and  of  any  am- 
pere capacity,  the  load  being  regulated  by  switching 
more  or  less  of  the  lamps  in  circuit  by  means  of  the 
.single  pole  switches,  L.  The  indicating  wattmeter 
may  be  of  5  or  10  ampere  capacity,  and  can  be  conveni- 
ently mounted  in  a  horizontal  position  on  a  swinging 
bracket;  the  current  transformer  being  of  a  5  or  10 
to  i  ratio,  or  if  desired,  several  current  transformers  of 


Fig.  96. 

•different  ratios  may  be  used.  For  testing  no-volt  watt- 
hour  meters  of  capacities  not  greater  than  the  capacity 
of  the  indicating  wattmeter,  the  d.p.d.t.  switch  S"  is 
thrown  in  the  dowhward  position,  thus  putting  poten- 
tial on  the  loo-volt  tap  of  the  indicating  wattmeter  and 
on  the  potential  winding  of  the  watt  hour  meter 
through  the  variable  resistance ;  at  the  same  time  the 
t.p.d.t.  switch  S'  is  thrown  down,  thus  connecting  the 
indicating  wattmeter  directly  into  the  circuit.  By 
throwing  S'  up,  the  current  transformer  is  connected 
into  circuit  when  it  is  desired  to  test  higher  capacity 
meters.  The  correct  load,  as  near  as  possible,  is  ob- 


MAINTENANCE  AXD  TESTING  141 

tained  by  closing  the  switches  L,  and  a  finer  adjust- 
ment is  accomplished  by  means  of  the  variable  resist- 
ance shown  in  the  diagram.  This  variable  resistance 
is  most  conveniently  made  up  by  wrapping  a  bare 
resistance  wire  on  a  suitable  mandrel  and  having  a 
sliding  contact  which  will  not  interrupt  the  circuit  in 
passing  from  one  turn  of  the  wire  to  the  next.  By 
means  of  this  variable  resistance,  the  tester  can  hold 
the  load  on  the  wattmeter  constant  while  the  test  is 
being  made. 

For  testing  2oo-volt  meters,  the  switch  S"  is 
thrown  in  the  upward  position;  and  S'  is  thrown  down 
or  up  according  to  whether  the  meter  in  test  is  below 
or  above  the  capacity  of  the  indicating  wattmeter. 

For  testing  5oo-volt  meters  the  switch  S  is  closed,, 
which  puts  the  potential  winding  of  the  watt  hour 
meter  directly  across  the  5oo-volt  tap  of  the  compen- 
sator, at  the  same  time  putting  the  potential  coil  of 
the  indicating  wattmeter  across  the  5<DO-volt  circuit 
in  series  with  the  multiplier. 

In  testing  meters  on  loads  of  low  power  factors,, 
suitable  reactances  can  be  substituted  for  the  ordinary 
lamp  bank  (arc  lamp  reactances  can  sometimes  be  con- 
veniently used  for  this  purpose),  or  the  potential  wind- 
ings of  the  meter  may  be  excited  from  a  different  phase 
of  a  three-phase  system  from  that  which  is  supply- 
ing the  load ;  in  this  case  the  power  factor  will  be  50 
per  cent,  and  may  be  either  lagging  or  leading,  depend- 
ing upon  which  phase  is  used  for  exciting  the  potential 
winding.  In  lagging  the  meter  for  low  power  factors,, 
a  two-phase  system  may  be  used,  exciting  the  potential 
winding  from  one  phase  and  furnishing  current  from 
the  other,  in  which  case  the  disc  should  remain  station- 
ary with  full  load  current  flowing. 

In  order  to  determine  which  phase  of  a  three- 
phase  system  to  use  .for  exciting  the  potential  wind- 
ings to  get  a  lagging  power  factor,  and  which  phase 
to  use  in  order  to  get  leading  power  factor,  simply 
connect  a  small  reactance  coil  in  the  place  of  the  lamp 
bank  (if  such  a  load  is  employed),  and  then  connect  the 


142 


THE   WATTHOUR   METER 


potential  winding  of  the  meter  first  to  one  phase  and 
then  to  the  other.  The  meter  will  run  slower  on  the 
phase  giving  a  lagging  power  factor. 

Where  a  great  number  of  watthour  meters  of  the 
same  type  are  to  be  tested  (such  as  is  the  case  with 
large  distributing  companies  in  testing  new  meters), 
the  testing  stand  shown  in  Fig.  97  permits  of  very 
rapid  work,  since  a  meter  can  be  hung  in  place  and 


•connections  made  within  three  or  four  seconds.  The 
stand  consists  of  a  wooden  base  about  2  x  il/2  ft.,  upon 
which  is  mounted  another  vertical  2-in.  board  of  about 
the  same  dimensions.  Fig.  97  shows  the  elevation  and 
plan  views.  Three  "L-shaped"  terminals  are  brought 
out  through  the  vertical  board,  the  spiral  springs  being 
used  to  press  the  terminals  firmly  against  the  binding 
screws  of  the  meter's  connection  block. 


MAINTENANCE  AND  TESTING 


143 


Another  method,  employing  a  connection  board 
•essentially  the  same  as  shown  in  Fig.  96,  is  shown 
diagrammatically  in  Fig.  98.  Instead  of  using  a  lamp 
bank  for  loading  the  watthour  meter  in  test,  a  "phan- 
tom load"  transformer,  T,  is  used,  the  secondary  of 


Fie. 


which  is  capable  of  supplying  a  heavy  current  at  a 
very  low  potential,  thereby  necessitating  only  the 
small  resistance  coils,  L,  for  regulating  the  load.  This 
method  requires  only  a  small  amount  of  power  even 
in  the  case^BBIptrge  meters,  and  is  therefore  very 
economical.  ^^P 


144  THE   WATTHOUR    METER 

Testing  Polyphase  Meters. 

In  testing  polyphase  watthour  meters,  it  is  usually 
most  convenient  to  adjust  and  test  them  on  a  single- 
phase  circuit  as  simple  single-phase  meters;  a  poly- 
phase meter  so  tested  will  then  be  correct  for  poly- 
phase work.  The  current  coils  may  be  connected  in 
series  and  the  potential  coils  in  multiple  for  testing  as 
a  single-phase  meter;  when  tested  in  this  way  the 
constant  of  the  meter  should  be  divided  by  two,  since 
the  current  is  passing  through  both  elements  and  is 
consequently  being  registered  twice.  A  balanced  read- 
ing should  be  taken  on  both  elements  as  follows : 

Potential  should  be  put  on  both  elements  and  a 
load  put  on  the  current  coil  of  one  element,  the  number 
of  revolutions  which  the  disc  makes  in  a  given  time 
being  noted ;  the  current  coil  of  this  element  should 
then  be  disconnected  and  that  of  the  other  element 
connected  in  the  same  manner  with  the  same  load 
applied  for  the  same  length  of  time,  the  revolutions  of 
the  disc  again  being  noted.  The  revolutions  of  the 
disc  in  each  instance  should  be  exactly  the  same,  and 
if  any  variation  is  found,  the  element  whose  speed  is 
incorrect,  should  be  adjusted  as  described  in  Chap.  III. 

A  better  method  of  testing  polyphase  meters  is  to 
apply  polyphase  potential  to  the  potential  windings 
exactly  as  will  be  the  case  when  the  meter  is  in 
service.  With  such  connections,  a  load  is  placed  on 
one  element  and  the  meter  tested  as  though  it  were  a 
single  phase  meter,  using  the  disc  constant  as  stamped 
on  the  disc  (divided  by  the  ratio  of  the  current  trans- 
formers times  the  ratio  of  the  potential  transformer^). 
The  load  should,  then  be  taken  off  of  this  element  and 
the  other  loaded,  by  means  of  which  a  "balanced" 
reading  can  be  obtained,  proper  adjustments  being 
made  if 'the  elements  do  not  balance.  The  advantage 
of  testing  the  meter  with  polyphase^^tential  applied 
to  the  potential  windings  is  that  ^1  ^terference  of 
the  potential  winding  of  one  elem^B  R  that  of  the 
other  will  be  normal,  and  can  be  cqP^fnsated  for  to 
great  extent  in  the  calibration  of  the  meter. 


MAINTENANCE  AND  TESTING 


145 


A  three-phase,  four-wire  meter  can  be  tested 
exactly  the  same  as  a  three-phase,  three-wire  meter  by 
using  the  two  current  windings  which  are  wound  one 
on  each  element,  leaving  the  third  current  winding 
open-circuited.  The  third  winding  is  wound  on  both 
elements  and  when  such  a  meter  is  tested  on  single- 
phase  current  with  both  potential  coils  connected  in 
multiple  the  meter  will  run  at  double  speed  when  this 
winding  is  carrying  the  load. 

Polyphase  meters  should  always  be  calibrated  for 
50  per  cent  power  factor  as  well  as  for  unity  power 
factor,  since  they  are  almost  always  used  upon  circuits 
which  at  times  operate  under  low  power  factor  con- 
ditions. 

Meters  Used  With  Current  and  Potential  Transformers 

When  watthour  meters  are  used  in  connection 
with  "current,"  or  "series,"  transformers,  there  are  two 
possible  sources  of  error  which  may  ensue ;  one  being 
due  to  the  angular  displacement  between  the  primary 
and  secondary  currents  of  the  transformer  (this  dis- 
placement should  be  exactly  180  degrees),  and  the 
other  is  due  to  the  varying  ratio  of  the  transformer  at 


Fig,  99. 

various  loads.  The  first  of  these  two  sources  of  error 
is  negligible  except  in  the  case  of  low  power  factors, 
and  is  largely  compensated  for  by  the  angular  dis- 
placement introduced  by  the  potential  transformer,  as 
will  be  explained  later  in  this  chapter. 


146  THE   WATTHOUR   METER 

• 

Fig.  99  is  a  vector  diagram   showing  the   phase 

relations  of  the  currents  in  the  primary  and  secondary 
of  a  current  transformer;  IM  is  a  component  of  the 
primary,  or  line  current  which  acts  as  exciting  current 
for  the  transformer  and  is  responsible  for  both  errors 
above  mentioned.  In  the  figure, 

OI    =  the  primary  or  line  current, 
OI1  =  the  secondary  current, 
O<f>  =  the  magnetic  flux  in  the  transformer  core, 
OV  =  the  voltage  of  primary  winding, 
OV]=  the  voltage  of  the  secondary  winding, 
IN  =  the  magnetizing  current, 
NM=  the  energy  component  which  supplies  the 
losses  of  the  transformer  and  the  load. 

One  source  of  error  is  due  to  the  fact  that  OI  is 
not  exactly  180  degrees  displaced  from  OI1,  and  there- 
fore the  current  which  flows  through  the  meter  (from 
the  secondary  side),  will  not  have  the  proper  phase 
relation  with  respect  to  the  current  in  the  potential 
coils  of  the  meter.  As  already  stated,  however,  for  all 
practical  purposes  the  error  thus  introduced  is  neg- 
ligible except  in  the  case  of  low  power  factors,  and  in 
transformers  of  poor  design.  It  can  be  seen  by  refer- 
ring to  the  above  diagram  that  if  the  secondary  circuit 
has  the  proper  amount  of  inductance  to  cause  the 
secondary  current  OI1  to  lag  by  the  same  angle  that 
the  exciting  current,  IM,  lags,  that  the  secondary  cur- 
rent will  be  exactly  180  degrees  out  of  phase  with  the 
primary  current,  which  would  result  in  there  being  no 
error  from  this  cause. 

The  second  error  referred  to,  which  is  caused  by 
the  varying  ratio  of  the  transformer,  is  due  to  the 
exciting  current,  IM,  not  being  effective  in  inducing 
current  in  the  secondary  winding;  the  secondary  cur- 
rent being  induced  by  the  component,  OM,  of  the 
primary  current.  If  IM  varied  directly  as  the  primary 
current,  this  error  could  be  corrected  by  adjusting  the 
ratio  between  the  primary  and  secondary  turns;  such 
is  not  the  case,  however,  and  an  error  is  introduced. 


MAINTENANCE  AND  TESTING 


147 


Fig.  100  is  a  curve  showing  the  accuracy  of  a  well- 
designed  current  transformer.  In  calibrating  watthour 
meters  for  use  in  connection  with  current  transformers, 
the  meter  should  be  calibrated  to  register  correctly  on 
the  flat  part  of  the  curve.  There  will  then  be  a  slight 
error  at  either  end  of  the  curve,  that  is,  there  will  be 
an  error  on  very  light  loads  on  or  overloads,  but  if  the 
meter  is  carefully  calibrated  in  accordance  with  the 


Fie.  100. 


Fig.  101. 

curve  of  the  transformer  it  will  be  accurate  over  the 
greater  part  of  the  range,  and  the  error  at  either 
extreme  will  be  small. 

Fig.  100  shows  a  typical  calibration  curve  of  a 
good  current  transformer,  and  Fig.  101  shows  the  cali- 
bration curve  of  a  standard  induction  watthour  meter. 
These  two  curves  are  combined  as  shown  in  Fig.  102, 
the  resultant  curve,  B,  being  the  resultant  calibration 
curve  of  the  meter  when  used  in  connection  with  the 
transformer.  It  will  be  seen  that  if  the  meter  is  ad- 


148 


THE    WATTHOUR    METER 


justed  so  that  it  will  be  a  little  slow  on  full  load  (about 
0.5  per  cent),  and  if  the  light  load  adjustment  is  set 
so  that  the  meter  will  be  slightly  fast  (about  0.5  per 
cent)  on  10  per  cent  load,  the  resultant  curve  will  be 
more  nearly  correct,  and  when  a  high  degree  of 
accuracy  is  required,  this  is  recommended,  the  amount 
of  such  adjustment  being  determined  by  referring  to 
the  calibration  curve  of  the  transformer  with  which 
the  meter  is  to  be  used. 

It  should  be  remembered  that  a  current  trans- 
former must  always  have  a  load  on  its  secondary  side  ; 
if  the  meter  or  instrument  with  which  it  is  being 
used  should  be  disconnected  while  current  is  still  on  the 


Fie.  102. 

primary,  the  transformer  should  either  be  disconnected 
from  the  line,  or  else  have  its  secondary  short-circuited. 
If  the  secondary  is  left  open-circuited  there  will  be 
no  counter  magneto-motive  force  from  the  secondary, 
consequently  the  magnetic  flux  will  increase  to  such 
a  degree  that  it  will  cause  the  iron  core  to  become 
overheated  to  an  extent  that  may  injure  the  trans- 
former. 

The  load  carried  by  potential  transformers  is 
constant,  and  if  the  load  is  light,  the  error  in  the 
transformer  ratio  will  be  very  small.  The  secondary 
e.m.f.  of  the  potential  transformer  leads  the  primary 
e.m.f.  by  a  small  angle,  6,  Fig.  103 ;  the  angular  dis- 
placement referred  to  in  connection  with  current 
transformers  is  also  leading;  it  therefore  follows  that 
the  angular  displacement  in  a  potential  transformer 


MAINTENANCE  AND  TESTING 


149 


compensates,  in  a  large  degree,  for  the  angular  dis- 
placement in  the  current  transformer ;  if  this  angular 
displacement  is  the  same  for  both  the  current  and 
potential  transformers  the  error  from  this  source  will 
be  entirely  eliminated  from  the  meter  with  which  they 
are  used. 

The  angular  displacement  referred  to  depends 
upon  the  magnitude  and  character  of  the  load  imposed 
upon  the  transformer,  as  well  as  upon  its  design. 


Fte.  103. 

Fig.  103  shows  a  vector  diagram  of  the  regulation  of 
a  potential  transformer,  in  which 

OE=primary  e.m.f.,  . 
OE'=secondary  e.m.f., 
OI=primary  current, 
OI'=secondary  current, 
RI=total  resistance  drop, 
XI=total  reactance  drop, 

$=angular  displacement  between  primary  and 
secondary  e.m.f.'s. 

In  using  5-ampere  no-volt  meters  with  current 
and  potential  transformers  and  leaving  the  regular 
register  on  the  meter  it  is  necessary  to  use  a  multiply- 
ing constant,  which,  multiplied  by  the  register  reading, 
gives  the  kilowatt  hours  consumed.  This  multiplying 


150  THE   WATTHOUR    METER 

constant  is  obtained  by  multiplying  the  ratio  of  the 
current  transformer  by  the  ratio  of  the  potential  trans- 
former. 

In  order  to  obtain  a  multiplying  constant  of  10, 
loo  or  1,000  it  is  often  necessary  to  use  a  special  regis- 
ter and  to  change  the  disc  constant  of  the  meter.  The 
new  disc  constant  is  obtained  from  the  following  for- 
mula: 

100  x  register  ratio  x  transformer  ratio 
10,000  x  C 

in  which  C  is  the  multiplier  of  10,  100  or  1,000. 

Applying  the  above  formula  to  an  example  we 
will  take  the  case  of  a  5-ampere  meter  having  a  disc 
constant  of  K=.3,  and  used  with  a  20  :  i  ratio  poten- 
tial transformer  and  a  24  :  i  ratio  current  transformer, 
from  which  the  "transformer  ratio"  in  the  formula  will 
be  (20x24)^480:1.  Suppose  a  register  is  chosen 
having  a  ratio  of  662-3,  and  a  multiplier  (C)  of  100 
is  used.  Substituting  these  values  in  the  above  for- 
mula we  derive  a  value  of  K=.3i2,  which  should  be 
used  instead  of  K=.3,  which  would  of  course  result 
in  a  slightly  different  operating  speed  of  the  disc. 

Meter  Troubles 

Some,  of  the  most  common  troubles  encountered 
in  connection  with  watthour  meters  may  be  sum- 
marized as  follows : 

Excessive  Vibration — If  a  meter  is  placed  in  such 
a  position  as  to  be  subject  to  excessive  vibration, 
creeping  often  results ;  vibration  is  also  severe  on  the 
lower  bearing.  This  trouble  can  in  many  cases  be 
remedied  by  placing  rubber  washers  between  the 
meter  and  the  wall  upon  which  it  is  supported ;  in 
severe  cases  a  spring  suspended  board  is  recom- 
mended. Wherever  possible,  meters  should  be  in- 
stalled in  places  that  are  entirely  free  from  vibration 
or  jarring  effects.  It  is  not  unusual  to  find  meters 
installed  near  doors  which  are  often  closed  and  opened, 
and  especially  is  this  bad  practice  where  the  \vall  or 
partition  is  of  light  construction. 


MAINTENANCE  AND  TESTING  151 

Humming    and    Rattling  of  Induction  Meters — 

This  trouble  is  usually  due  to  loose  laminations  in  the 
magnetic  circuit,  and  can  be  remedied  by  tightening 
them  up.  Rattling  may  also  be  due  to  a  vibiation  of 
the  disc  and  shaft  in  very  loosely  aligned  meters, 
which  trouble  can  usually  ^e  removed  by  carefully 
examining,  locating  and  tightening  the  exact  parts 
that  may  be  loose.  Excessive  humming  is  sometimes 
caused  by  the  potential  winding  being  loose  on  the 
potential  pole,  which  trouble  can  be  easily  remedied 
by  driving  small,  flat  wooden  wedges  between  the 
insulating  sleeve  (upon  which  the  coil  is  mounted) 
and  the  core. 

Humming  is  not  an  inherent  phenomenon  of  the 
induction  meter,  and  trouble  from  this  source  can 
always  be  traced  to  some  simple  mechanical  defect. 
It  sometimes  happens  that  the  wall  upon  which  the 
meter  is  mounted  acts  as  a  ''sounding  Voard,"  thus 
magnifying  the  humming  of  the  meter.  This  can  be 
corrected  by  the  use  of  rubber  wr.shers  as  above  men- 
tioned for  excessive  vibration.  It  is  best,  however,  to 
remove  the  meter  to  a  place  that  will  not  be  subject 
to  such  trouble. 

Weakening  of  the  Retarding  Magnets — Magnets, 
after  having  been  in  service  for  som.e  time,  may  be- 
come weak,  due  to  the  "aging"  of  the  steel;  this 
should  not  occur,  however,  if  they  have  been  thor- 
oughly and  properly  treated  before  leaving  the  factory. 
Weakening  due  to  aging  is  a  very  serious  defect  and 
shows  the  lack  of  proper  methods  or  care  in  their 
manufacture.  Such  trouble  should  be  guarded  against 
in  the  selection  of  meters.  The  retarding  magnets 
may  also  be  weakened  by  the  effects  of  powerful 
stray  fields,  or  by  heavy  short  circuits  on  the  "load" 
side  of  the  meter. 

The  retarding  magnets  should  never  be  moved 
closer  than  one-quarter  of  an  inch  to  the  periphery 
of  the  disc,  because  if  they  are  there  will  be  a  leakage 
of  magnetic  flux  around  the  disc,  from  pole  to  pole 
of  the  magnets,  thereby  decreasing  the  number  of 


152  .          THE   WATTHOUR   METER 

lines  of  force  that  actually  cut  the  disc.  This  of 
course  will  have  the  same  effect  as  the  weakening  of 
the  magnets,  and  will  cause  the  meter  to  run  fast. 
Magnets  that  will  not  produce  the  necessary  retarding 
effect  when  moved  within  a  quarter  of  an  inch  of  the 
edge  of  the  disc  are  too  weak  and  they  should  be 
discarded. 

Sometimes  it  is  found  necessary  to  place  iron 
shields  around  the  damping  system  of  meters  which 
are  not  already  provided  with  such  a  protection  against 
stray  fields,  and  when  this  is  done  the  meter  should 
be  re-calibrated,  since  the  proximity  of  the  iron  shield 
may  allow  a  leakage  of  flux  which  would  result  in  the 
same  trouble  as  placing  the  magnets  too  near  the 
periphery  of  the  disc. 

Bent  Shafts  and  Buckled  Discs — These  troubles 
may  be  due  to  one  of  three  causes;  by  abuse,  by  the 
effects  of  short  circuits  of  a  severe  nature,  or  to  faulty 
manufacture ;  the  only  remedy  is  to  install  new 
parts. 

Creeping — Creeping  may  be  due  to  "over-com- 
pensation" of  the  light  load  adjustment,  vibration, 
high  voltage,  or  a  combination  of  any  or  all  of  these 
effects,  or  in  commutating  meters  by  the  external  re- 
sistance being  short-circuited.  Some  types  of  induc- 
tion meters  have  two  small  holes  punched  in  their 
discs,  the  holes  being  diametrically  opposite.  When 
the  part  of  the  disc  which  has  the  hole  in  it  comes 
under  the  influence  of  the  electrical  element,  the 
torque  is  thereby  sufficiently  decreased  to  allow  the 
disc  to  stand  in  that  position  when  there  is  no  current 
flowing  in  the  series  coils.  This  method  very  effec- 
tually prevents  "creeping,"  but  it  does  not  affect  the 
accuracy  of  the  meter. 

Creeping  in  the  commutating  type  of  meter  can 
be  very  effectively  eliminated  by  clamping  over  the 
edge  of  the  disc  a  small  piece  of  U-shaped  soft  iron 
wire;  when  the  piece  of  wire  comes  under  the  in- 
fluence of  the  retarding  magnet  the  attraction  of  the 
magnet  tends  to  hold  the  disc  in  that  particular  posi- 


MAINTENANCE  AND  TESTING  153 

tion,  therefore  preventing  creeping  on  no  load.  The 
size  of  the  clip  can  be  so  selected  that  it  will  pre- 
vent creeping,  but  which  will  not  prevent  the  meter 
from  starting  on  light  loads  nor  affect  the  light  load 
accuracy. 

A  modification  of  the  last  named  method  con- 
sists in  attaching  a  piece  of  iron  wire  to  the  shaft  of 
the  meter  in  such  a  manner  that  its  free  end  extends 
out  radially  and  comes  under  the  influence  of  the 
retarding  magnets ;  the  effect  of  the  wire  can  be 
varied  by  bending  it  so  that  its  free  end  comes  closer 
to  or  further  from  the  magnets. 

Defective  Jewels — The  simplest  and  probably  the 
easiest  way  of  detecting  roughness  or  defectiveness  in 
the  jewel  bearing  is  to  take  the  point  of  a  sharp  needle 
and  gently  "feel"  the  entire  surface  of  the  jewel.  A 
fracture  or  any  roughness  can  thus  be  detected.  In 
this  connection  it  might  be  stated  that  one  of  the 
best  materials  for  cleaning  the  jewels  and  pivots  is 
the  pith  from  a  cornstalk.  After  the  jewel  and  pivot 
have  been  thoroughly  cleaned,  the  pivot  should  be 
wiped  with  a  clean  rag  which  has  been  moistened  with 
a  high  grade  of  watch  oil,  but  under  no  conditions 
should  it  be  flooded  with  oil. 

Changing  Position  of  Commutator  on  Shaft — If 
the  commutator  is  shifted  from  its  correct  position  on 
the  shaft  it  will  cause  the  meter  to  run  slow ;  if  it  is 
shifted  90  degrees  the  meter  will  stop,  and  if  shifted 
more  than  90  degrees  the  meter  will  run  backward. 

Backward  Rotation  of  Commutating  Meters  on 
Light  Load — It  may  sometimes  be  found  that  the 
commutator  meter  will  run  in  a  reverse  direction  on 
light  loads,  while  on  heavier  loads  it  will  run  in  the 
proper  direction.  Such  a  trouble  will  be  found  due 
to  a  reversed  connection  of  the  compensating  field, 
so  that  instead  of  helping  the  main  field  out,  its  action 
is  differential.  Care  should  therefore  be  taken  to  see 
that  the  compensating  field  is  properly  connected. 

Open-Circuited  Armatures — The  current  in  enter- 
ing the  commutator  divides  at  each  brush  and  flows 


154  THE   WATTHOUR    METER 

through  the  armature  in  two  multiple  paths  of  equal 
resistance;  if  one  of  these  paths  is  opened,  it  will 
therefore  be  seen  that  the  equivalent  resistance  of 
the  armature  will  be  doubled,  which  will  cause  the 
meter  to  run  at  about  half  speed.  The  same  result 
may  be  accomplished  by  using  an  ordinary  16  candle- 
power  lamp  and  moving  the  connection  from  one  bar 
to  the  other;  the  lamp  will  not  light  until  after  the 
defective  coil  has  been  passed. 

The  defective  coil  can  very  easily  be  located  with 
a  voltmeter.  Apply  the  normal  voltage  to  the  two 
brushes  and  with  one  of  the  voltmeter  leads  per- 
manently attached  to  one  brush,  move  the  other  lead 
over  the  commutator  from  bar  to  bar,  during  which 
operation  no  deflection  will  be  indicated  on  the  volt- 
meter until  the  defective  coil  is  reached,  unless  the 
movable  voltmeter  terminal  happens  to  be  passed 
over  that  half  of  the  armature  in  which  there  'are 
no  open-circuits. 

Friction  in  Upper  Bearing — It  sometimes  happens 
that  the  upper  bearing  is  pressed  down  too  tightly 
against  the  upper  end  of  the  shaft,  thereby  causing 
excessive  friction  which  will  result  in  the  meter  run- 
ning slow  on  light  loads ;  this  trouble  is  easily  reme- 
died by  loosening  the  binding  screw  and  raising  the 
bearing  slightly. 

Friction   in   the   Registering   Mechanism — If   the 

registering  mechanism  is  allowed  to  accumulate  dirt 
and  grease  it  will  develop  undue  friction ;  care  should 
therefore  be  taken  to  see  that  the  registers  are  kept 
in  good,  clean  condition. 

Dirt  on  Meter  Disc — Small  pieces  of  trash  or  dirt 
on  the  meter  disc  will,  if  they  come  in  contact  with 
the  retarding  magnets,  or  the  stationary  element,  act 
as  a  brake  on  the  meter. 


CHAPTER  VIII. 
RATES. 

The  fixing  of  a  scale  of  rates  for  the  sale  of  elec- 
trical energy  which  will  be  fair  to  both  the  consumer 
and  the  distributing  company  is  a  difficult  problem, 
which  will  here  be  briefly  outlined.  We  will  confine 
ourselves  to  showing  why  it  is  that  electrical  energy 
cannot  be  sold  to  all  classes  of  consumers  at  the  same 
rate,  and  further  to  reproduce  schedules  of  rates  as 
adopted  by  some  of  the  leading  distributing  companies 
throughout  the  United  States. 

Electrical  energy  cannot  be  stored  in  large  quan- 
tities except  at  a  great  expense,  but  must  ordinarily 
be  "manufactured"  as  the  demand  necessitates.  For 
this  reason,  it  is  necessary  for  the  distributing  com- 
pany to  provide  generating  and  distributing  equip- 
ment to  handle  the  maximum  demand  or  "peak  load," 
and  since  the  peak  load  usually  lasts  for  only  a  few 
hours,  the  system  is  being  operated  for  the  greater 
part  of  the  day  at  a  production  much  below  its  full 
capacity.  The  operating  expenses,  however  (except 
fuel,  etc.),  remain  practically  the  same,  as  do  the  fixed 
charges,  the  maintenance,  depreciation  and  interest  on 
the  investment.  The  charges  which  are  proportional 
to  the  quantity  of  energy  being  generated,  such  as 
water,  fuel,  etc.,  constitute  the  smaller  portion  of  the 
total  cost,  therefore  it  is  evident  that  the  distributing 
company  can  sell  electrical  energy  to  consumers  using 
it  for  a  good  many  hours  per  day  cheaper  than  it  can 
to  consumers  using  it  for  only  a  few  hours  per  day, 
since  the  revenue  from  the  "long  hours"  customer  will 
be  greater  even  at  a  lower  rate,  while  the  manufac- 
turing expense  will  not  be  much  greater. 

To  illustrate  the  above  statements  take  as  an 
example  two  consumers,  each  taking  the  same  amount 
of  power,  but  one  of  which  takes  this  power  for  ten 
hours  per  day  while  the  other  takes  it  for  two  hours 


156  THE    WATTHOUR    METER 

per  day.  The  equipment  necessary  to  supply  each  cus- 
tomer is  practically  the  same,  as  are  also  the  fixed 
•charges.  A  profit  of  one  cent  per  kilowatt-hour  above 
operating  expenses  from  the  customer  taking  power 
for  ten  hours  per  day  would  be  more  profitable  to  the 
distributing  company  than  would  a  profit  of  two  or 
three  cents  per  kilowatt-hour  from  the  customer  tak- 
ing power  for  only  two  hours.  In  the  first  case  the 
.gross  profit  above  operating  expenses  would  be  ten 
•cents  per  kilowatt  per  day,  while  in  the  second  case 
it  would  be  four  or  six  cents.  Suppose  that  the  fixed 
•charges  amounted  to  4  cents  per  kilowatt  per  day,  the 
two  hour  customer  would  yield  a  profit  of  only  two 
cents  per  kilowatt  demand  per  day,  while  the  ten 
hour  customer,  at  a  rate  of  2  cents  lower,  would  yield 
a  profit  of  6  cents  per  kilowatt  demand  per  day,  or 
three  times  as  much.  In  the  case  of  very  small  con- 
sumers, the  cost  of  bookkeeping,  meter  reading,  test- 
ing, etc.,  is  disproportionately  high  ;  the  losses  in  the 
-distributing  system  are  also  out  of  proportion,  which 
further  increases  the  cost  of  supplying  energy  to  the 
small  consumer. 

The  distributing  company  can  afford  to  sell  energy 
during  the  "off-peak"  period  cheaper  than  it  can  dur- 
ing the  hours  of  the  peak  load,  since  during  the  period 
of  maximum  demand,  the  equipment  is  usually  taxed 
to  its  utmost.  An  increase  in  the  peak  load  means  an 
increase  in  the  equipment  or  else  a  greater  strain  and 
•depreciation  on  the  present  installation,  while  an  in- 
crease in  the  "off-peak"  load  can  be  readily  handled 
with  the  resulting  increase  in  revenue.  Generating  and 
distributing  equipment  has  to  be  provided  of  sufficient 
capacity  to  take  care  of  the  peak  load.  During  off-peak 
hours,  a  large  part  of  this  equipment  is  idle.  The 
charges  (maintenance,  depreciation  and  interest  on  the 
investment)  due  to  this  excess  equipment  provided  to 
handle  the  peak  load  are  properly  chargeable  to  the 
cost  of  manufacture  during  peak  load  hours,  which 
makes  the  cost  of  producing  a  kilowatt-hour  during 
this  time  high. 


RATES  157 

Since  the  cost  of  manufacture  is  higher  during  the 
peak  load,  it  is  only  fair  and  just  that  the  consumers 
demanding  current  at  this  time  should  pay  a  corre- 
spondingly higher  rate. 

Another  point  which  should  be  borne  in  mind 
when  determining  the  rates  made  to  different  custom- 
ers is  the  nature  of  the  load  with  regard  to  the  power 
factor.  The  capacity  of  the  generating  and  distribut- 
ing equipment  is  limited  by  the  amount  of  current  to 
be  handled,  from  which  it  is  evident  that  the  cost  of 
supplying  energy  to  a  load  of  low  power  factor  will  be 
higher  than  the  cost  of  supplying  a  similar  load  (in 
kilowatts)  of  a  higher  power  factor.  Especially  is  this 
true  during  the  period  of  maximum  demand. 

REPRESENTATIVE  SCHEDULES  OF  RATES. 

The  Commonwealth  Edison  Co.,  of  Chicago,  111. 

Schedule  A. — Regular  Lighting   Rate. 

The  following  is  the  regular  rate  for  electricity  for  light- 
ing purposes,  or  upon  an  interior  distributing  circuit  carrying 
electricity  for  lighting  and  also  for  heating  or  power  through 
the  same  meter,  as  measured  by  a  meter  or  meters  owned 
and  installed  by  the  company: 

Thirteen  cents  (13c)  per  kilowatt  hour  for  all  electricity 
consumed  in  each  month  up  to  and  including  an  amount  that 
would  be  equal  to  thirty  hours'  use  of  the  consumer's  maximum 
demand  in  such  month,  and  seven  cents  (7c)  per  kilowatt  hour 
for  all  electricity  consumed  in  such  month  in  excess  of  that 
amount. 

Maximum  recording  meters  will  be  installed  by  the  com- 
pany for  the  purpose  of  ascertaining  the  maximum  demand,, 
except  where  the  capacity  of  the  consumer's  installation  is 
less  than  one  kilowatt,  in  which  case  the  maximum  demand 
will  be  estimated. 

A  discount  of  one  cent  per  kilowatt  hour  on  the  con- 
sumer's total  monthly  consumption  will  be  allowed  on 
monthly  bills  paid  on  or  before  ten  days  after  their  respective 
dates. 

The  rate  stated  in  this  schedule  A  covers  and  includes, 
for  incandescent  lighting,  the  free  installation  and  use  of  the 
proper  supply  of  incandescent  lamps  of  the  company's  pres- 
ent standard  carbon  filament  types,  and  of  the  same  voltage,. 


158  THE   WATTHOUR   METER 

efficiency  and   candlepower  as   the   incandescent   lamps   now 
furnished  by  the  company. 

An  abatement  or  reduction  of  one-half  cent  (l/2c.)  per 
kilowatt-hour  from  the  aforesaid  rate  shall  be  allowed  to  a 
consumer  furnishing,  maintaining  and  renewing  all  the  lamps 
or  other  forms  of  electric  illuminants  used  by  him. 

Schedule    B. — Regular    Power    Rate. 

The  following  is  the  regular  rate  for  electricity  used  for 
power  purposes  exclusively,  as  measured  by  a  meter  or 
meters  owned  and  installed  by  the  company: 

Eleven  cents  (lie)  per  kilowatt  hour  for  all  electricity 
consumed  in  each  month  up  to  and  including  an  amount  that 
would  be  equal  to  thirty  hours'  use  of  the  consumer's  maximum 
demand  in  such  month;  and  six  cents  (6c)  per  kilowatt  hour 
for  all  electricity  consumed  in  such  month  in  excess  of  that 
amount. 

When  the  electricity  is  taken  from  the  company's  direct 
current  system,  the  greatest  number  of  kilowatts  used  at  one 
time  (the  peak  of  the  load)  in  any  month  shall  be  deemed  the 
maximum  demand  for  such  month;  and  maximum  recording 
meters  will  be  furnished  by  the  company  for  the  purpose  of 
ascertaining  the  maximum  demand,  except  where  the  capacity 
of  the  consumer's  installation  is  less  than  one  kilowatt,  in 
which  case  the  maximum  demand  will  be  estimated. 

When  the  electricity  is  taken  from  the  company's  alter- 
nating current  system,  the  maximum  demand  for  any  month 
shall  be  the  number  of  kilowatts  equal  to  a  percentage  of  the 
total  kilowatt  capacity  represented  by  all  motors  connected, 
which  percentage  shall  be  in  accordance  with  the  following 
table  of  percentages: 

Where  installations  are  under  10  horsepower,  and  only 
one  motor  is  used  85% 

Where  installations  are  under  10  horsepower,  and  more 
than  one  motor  is  used  '.  75% 

Where  installations  are  from  10  horsepower  to  50  horse- 
power, both  inclusive  (irrespective  of  number  of 
motors)  65% 

Where  installations  are  over  50  horsepower  (irrespective 

of  number  of  motors)    55% 

The  horsepower  capacity  of  any  alternating  current 
motor  or  motors  shall  be  assumed  to  be  that  which  is  in- 
dicated by  the  manufacturer's  standard  nominal  rating  or 
ratings;  and  each  horsepower  shall  be  deemed  to  be  equal 


RATES  159 

to  seven  hundred  and  forty-six  watts.  The  company  shall, 
however,  have  the  right  ,from  time  to  time,  to  test  any  such 
motor  or  motors,  and  if  it  be  found  on  any  such  test  that  the 
actual  horsepower  used  by  such  motor  or  motors  exceeds  its 
or  their  rated  capacity,  the  kilowatt  equivalent  of  the  maxi- 
mum horsepower  actually  used  shall  constitute  the  consumer's 
maximum  demand. 

A  discount  of  one  cent  (Ic.)  per  kilowatt-hour  on  the  con- 
sumer's total  monthly  consumption  will  be  allowed  on 
monthly  bills  paid  on  or  before  ten  days  after  their  respective 
dates. 

The  consumer  shall  pay  to  the  company  each  month  not 
less  than  fifty  cents  (50c.)  per  horsepower,  or  fraction 
thereof,  in  rated  capacity  of  motor  or  motors  connected. 

Schedule    C. — Wholesale    Rates    for    Electricity. 

Any  consumer  entering  into  a  written  contract  to  use  the 
company's  electricity  for  either  lighting  or  power,  or  both, 
for  a  period  of  not  less  than  five  years  in  any  single  premises 
occupied  by  him,  will,  at  his  option,  be  given  a  wholesale  rate 
for  such  premises,  in  lieu  of  the  rates  stated  in  Schedules  A 
and  D,  which  wholesale  rate  shall  consist  of  both  a  primary 
and  a  secondary  charge  in  accordance  with  the  following 
specification  of  charges: 

Direct  Current. — Contract  Without  Guaranty. 

Primary  Charges. 
For  Each   Month: 
$3.20  per   kilowatt   of   the   consumer's   maximum   demand   in 

such  month  up  to  and  including  20  kilowatts. 
$2.50  per  kilowatt  of  the  excess  of  the  consumer's  maximum 

demand  in  such  month  over  20  and  up  to  and  including 

50  kilowatts. 
$2.20  per  kilowatt  of  the  excess  of  the  consumer's  maximum 

demand  in  such  month  over  50  kilowatts. 

Secondary   Charges. 
For  Each  Month: 

6c  per  kilowatt-hour  for  the   consumption   in  such  month 

up  to  and  including  2000  kilowatt  hours. 
3c  per  kilowatt-hour  for  the  excess  consumption   in  such 
month  over  2000  and  up  to  and  including  5000  kilowatt 
hours. 

1.4c  per  kilowatt-hour  for  the  excess  consumption  in  such 
month  over  5000  kilowatt-hours. 


160  THE   WATTHOUR    METER 

Contract  with   Guaranty. 

If  the  consumer  will  guarantee  that  his  maximum  de- 
mand in  each  year  of  the  contract  term  shall  be  not  less  than 
200  kilowatts,  the  following  primary  and  secondary  charges 
will  be  made: 

Primary  Charges. 
$28.00  per  kilowatt  per  year  reckoned  upon  200  kilowatts,  the 

guaranteed  maximum  demand;   and 

$25.00  per  kilowatt  per  year  for  the  excess,  if  any,  over  200 
kilowatts  of  the  consumer's  actual  maximum  demand 
recorded  in  the  year. 

Such  primary  charges  for  each  year  to  be  paid  by  the 
consumer  in  installments  as  follows: 

At  the  end  of  each  month  he  shall  pay  $2.33  1-3  per  kilo- 
watt reckoned  upon  200  kilowatts,  and  $2.08  1-3  per  kilowatt 
for  the  excess,  if  any,  over  200  kilowatts  of  the  maximum 
demand  recorded  in  the  year  previously  to  that  time. 

At  the  end  of  the  year  he  shall  pay  the  difference,  if 
any,  between  the  sum  of  the  prescribed  monthly  installments 
for  the  year,  and  the  amount  constituting  the  full  primary 
charge  for  the  year. 

Secondary   Charges. 
For  Each  Month: 

6c  per   kilowatt-hour   for   consumption    in   such   month   up 

to  and   including  2000   kilowatt-hours. 

3c  per  kilowatt-hour  for  the  excess  consumption  in  such 
month  over  2000  and  up  to  and  including  5000  kilowatt- 
hours. 

1.4c  per  kilowatt-hour   for   the   excess  consumption   in   such 
month  over  5000  kilowatt-hours. 

Alternating  Current  Transformed. — Contract  Without 
Guaranty. 

Primary    Charges. 
For   Each    Month: 

$3.20  per  kilowatt  of  the  consumer's  maximum  demand  in 
such  month  up  to  and  including  20  kilowatts. 

$2.20  per  kilowatt  of  the  excess  of  the  consumer's  maximum 
demand  in  such  month  over  20  and  up  to  and  including 
50  kilowatts. 

$2.00  per  kilowatt  of  the  excess  of  the  consumer's  maximum 
demand  in  such  month  over  50  kilowatts. 


RATES  161 

Secondary    Charges. 
For  Each  Month: 

6c  per  kilowatt-hour  for   the   consumption   in   such   month 

up  to  and  including  2000  kilowatt-hours. 
3c  per  kilowatt-hour  for  the   excess   consumption   in   such 
month  over  2000  and  up  to  and  including  5000  kilowatt- 
hours. 

l.lc  per  kilowatt-hour  for  the  excess  consumption  in  such 
month  over  5000  and  up  to  and  including  30,000  kilowatt- 
hours. 

.9c  per  kilowatt-hour  for  the  excess  consumption  in  such 
month  over  30,000  kilowatt-hours. 

Contract  With  Guaranty. 

If  the  consumer  will  guarantee  that  his  maximum  demand 
in  each  year  of  the  contract  term  shall  be  not  less  than  200 
kilowatts,  the  following  primary  and  secondary  charges  will 
be  made: 

Primary  Charges. 

$26.00  per  kilowatt  per  year  reckoned  upon  200  kilowatts,  the 

guaranteed  maximum  demand;   and 

$21.50  per  kilowatt  per  year  for  the  excess,  if  any,  over  200 
kilowatts  of  the  consumer's  actual  maximum  demand 
recorded  in  the  year. 

Such  primary  charges  for  each  year  to  be  paid  by  the 
consumer  in  installments  as  follows: 

At  the  end  of  each  month  he  shall  pay  $2.16  2-3  per 
kilowatt  reckoned  upon  200  kilowatts,  and  $1.75  1-6  per 
kilowatt  for  the  excess,  if  any,  over  200  kilowatts  of  the 
maximum  demand  recorded  in  the  year  previously  to  that 
time. 

At  the  end  of  the  year  he  shall  pay  the  difference,  if  any, 
between  the  sum  of  the  prescribed  monthly  installments  for 
the  year,  and  the  amount  constituting  the  full  primary  charge 
for  the  year. 

Secondary  Charges. 
For  Each   Month: 

6c  per  kilowatt  for  the  consumption  in  such  month  up  to 

and  including  2000  kilowatt-hours. 

3c  per  kilowatt-hour  for  the  excess  consumption  in  such 
month  over  2000  and  up  to  and  including  5000  kilowatt- 
hours. 


162  THE   WATTHOUR    METER 

l.lc  per  kilowatt-hour  for  the  excess  consumption  in  such 
month  over  5000  and  up  to  and  including  30,000  kilowatt 
hours. 

.9c  per  kilowatt-hour   for  the  excess   consumption   in   such 
month  over  30,000  kilowatt  hours. 

Alternating    Current    Untransformed. — Contract    With 
Guaranty. 

If  the  consumer  will  guarantee  that  his  maximum  demand 
in  each  year  of  the  contract  term  shall  be  not  less  than  200 
kilowatts,  the  following  primary  and  secondary  charges  will 
be  made: 

Primary    Charges. 
$25.00  per  kilowatt  per  year  reckoned  upon  200  kilowatts,  the 

guaranteed  maximum  demand;   and 

$20.50  per  kilowatt  per  year  for  the  excess,  if  any,  over  20G 
kilowatts  of  the  consumer's  actual  maximum  demand 
recorded  in  the  year. 

Such  primary  charges  for  each  year  to  be  paid  by  the 
consumer  in  installments  as  follows: 

At  the  end  of  each  month  he  shall  pay  $2.08 1-3  pel 
kilowatt  reckoned  upon  200  kilowatts,  and  $1.70  5-6  per  kilo- 
watt for  the  excess,  if  any,  over  200  kilowatts  of  the  maximum 
demand  recorded  in  the  year  previously  to  that  time. 

At  the  end  of  the  year  he  shall  pay  the  difference,  if  any. 
between  the  sum  of  the  prescribed  monthly  installments  for 
the  year,  and  the  amount  constituting  the  'full  primary 
charge  for  the  year. 

Secondary  Charges. 
For   Each    Month: 

6c  per  kilowatt-hour   for  the   consumption   in   such   month 

up  to  and  including  2000  kilowatt-hours. 
2.7c  per  kilowatt-hour  for   the  excess   consumption  in   such 
month  over  2000  and  up  to  and  including  5000  kilowatt- 
hours. 

Ic  per  kilowatt-hour  for  the  excess  consumption  in   sucb 
month  over  5000  and  up  to  and  including  30,000  kilowatt 
hours. 
.8c  per  kilowatt-hour   for  the   excess   consumption   in   such 

month  over  30,000  kilowatt-hours. 

Bills  for  both  primary  and  secondary  charges  will  be  ren 
dered  monthly  and  a  discount  of  ten  per  cent.  (10%)  upon  the. 


RATES  163 

secondary   charges   will   be   allowed   on   all   bills   paid   on   or 
before  ten  days  after  their  respective  dates. 

Schedule  U. — Automobile  Charging   in   Private  Garages. 

The  rate  for  electricity  for  charging  automobiles  in  pri- 
vate garages  is  either  the  regular  power  rate  specified  in 
Schedule  B,  or  the  power  rate  under  contract  for  one  year  or 
longer  specified  in  Schedule  D  as  the  consumer  may  prefer, 
subject,  however,  to  the  following  additional  provisions: 

The  net  minimum  charge  to  be  paid  by  the  consumer 
each  month  shall  be  not  less  than  sixty-six  and  two-thirds 
cents  (66  2-3c)  for  each  kilowatt  of  the  consumer's  maximum 
demand  in  such  month,  and  no  monthly  bill  shall  be  less  than 
one  dollar  and  fifty  cents  ($1.50).  Where  alternating  current 
charging  boards  are  used  no  monthly  bill  shall  be  less  than 
one  dollar  and  fifty  cents  ($1.50)  for  each  charging  board. 

Schedule   V. — Automobile   Charging    in    Public   Garages. 

The  rate  for  electricity  for  charging  automobiles  in  public 
garages  is  either  the  regular  power  rate  specified  in  Schedule 
B,  or  the  power  rate  under  contract  for  one  year  or  longer, 
specified  in  Schedule  D,  as  the  consumer  may  prefer,  subject, 
however,  to  the  following  additional  privisions: 

If  the  consumer  agrees  not  to  make  use  of  the  company's 
service  for  this  purpose  during  the  two  hours  of  the  day  be- 
tween four  and  six  o'clock  P.  M.,  his  net  rate  for  electricity 
furnished  for  charging  automobiles  shall  not  exceed  five  cents 
(5c.)  per  kilowatt-hour. 

Where  alternating  current  charging  boards  are  used  no 
monthly  bill  shall  be  less  than  one  dollar  and  fifty  cents 
($1.50)  for  each  charging  board. 

Schedule  W. — Rates  for  "Throw-Over"  Switch  Service. 

Where  a  consumer  s  premises  are  supplied  with  electricity 
either  for  light  or  power,  or  both,  from  some  plant  in  the 
building  in  which  the  premises  are  situated  (whether  such 
plant  belongs  to  the  consumer  or  not),  and  such  consumer 
desires  to  be  in  a  position  to  use,  or  in  fact  uses,  the  com- 
pany's electrical  service,  not  regularly  but  only  occasionally 
and  during  the  temporary  break-down  or  cessation  of  such 
plant;  or  where  a  consumer's  premises  are  supplied  with 
power  of  any  kind  from  any  plant  in  the  building  in  which  the 
premises  are  situated  (whether  such  plant  be  an  electric  plant 
or  not,  or  be  owned  by  the  consumer  or  not),  and  such  con- 
sumer desires  to  be  in  a  position  to  use,  or  in  fact  uses,  the 


164  THE   WATTHOUR   METER 

company's  electrical  power  service,  not  regularly  but  only 
occasionally  and  during  the  temporary  bread-down  or  cessa- 
tion of  such  plant,  the  consumer  will  be  charged  and  must  pay 
to  the  company  for  such  emergency  service  the  rate  herein- 
after in  this  schedule  provided,  to-wit: 

Such  rate  will  be  that  specified  in  Schedule  A.  D.  or  E,  ac- 
cording to  the  purpose  for  which  the  service  is  used,  with  the 
additional  requirement  that  the  consumer  shall  pay,  irre- 
spective of  the  amount  of  his  consumption,  a  minimum 
monthly  charge  depending  upon  the  number  and  capacity  of 
lamps,  motors  and  other  apparatus  arranged  for  connection 
with  the  company's  service,  which  charge  shall  be  in  accord- 
ance with  the  following  table  of  minimum  charges: 

For  each  incandescent  lamp  so  connected,  ten  cents  (lOc) 
per  month  where  the  lamp  has  a  capacity  of  fifty  (50)  watts 
or  less,  at  rated  voltage,  and  at  the  rate  of  ten  cents  (lOc) 
per  month  for  fifty  (50)  watts  of  capacity  where  the  lamp  has 
a  capacity  exceeding  fifty  (50)  watts. 

For  each  arc  lamp  so  connected  one  dollar  ($1.00)  per 
month  where  the  lamp  has  a  capacity  of  five  hundred  (500) 
watts  or  less,  at  rated  voltage,  and  at  the  rate  of  one  dollar 
<$1.00)  per  month  for  five  hundred  (500)  watts  of  capacity 
where  the  lamp  has  a  capacity  exceeding  five  hundred  (500) 
watts. 

For  each  motor  so  connected,  other  than  a  motor  used 
for  operating  elevators,  hoists  or  similar  machinery,  one 
dollar  and  fifty  cents  ($1.50)  per  month  per  rated  horsepower 
of  such  motor. 

For  each  motor  so  connected  used  for  operating  eleva- 
tors, hoists  or  similar  machinery,  five  dollars  ($5.00)  per 
month  per  rated  horsepower  of  such  motor. 

The  company  will  furnish  emergency  service  under  this 
schedule  only  when  the  premises  are  situated  on  its  existing 
lines  having  the  requisite  capacity,  and  only  when  the  con- 
sumer signs  a  contract  for  the  service,  running  for  one  year 
or  longer  and  specifying  the  number  and  capacity  of  lamps, 
motors  or  other  electrical  apparatus  in  his  premises  that  are 
to  be  supplied  with  the  company's  electricity  during  such 
occasional  periods  and  providing  that  the  consumer  shall  so 
arrange  his  wiring  that  no  lamps,  motors  or  apparatus  other 
than  those  specified  in  the  contract  can  be  thrown  on  the  com- 
pany's service  by  means  of  switches,  or  otherwise.  For  the 
purpose  of  this  service  the  company  will  enter  its  service 
main  into  the  building  in  which  the  consumer's  premises  are 
situated  (providing  the  consumer,  in  case  he  shall  not  own 


RATES  165 

the  building,  shall  obtain  the  necessary  consent  from  the 
owner),  and  the  consumer  must,  at  his  own  expense,  install 
switches  and  such  other  equipment  as  may  be  necessary  for 
connecting  his  premises  with  such  service  main  at  the  point 
of  entry  into  the  building.  For  service  under  this  schedule 
the  company  will  not  furnish  lamps  or  renewals  for  the  same. 

The  Edison  Electric  Illuminating  Co.,  of  Boston,  Mass. 
Lighting    Rates — Commercial. 

Electricity  for  any  use  will  be  sold,  under  the  following 
schedule,  to  any  customer  who  has  signed  an  agreement  for 
electric  service,  embodying  the  terms  and  conditions  of  the 
company. 

A  price  of  12  cents  per  kilowatt-hour  will  be  charged  for 
all  electricity  furnished  under  this  schedule,  and  the  mini- 
mum charge  will  be  $1.00  per  month  per  meter. 

Power   Rates — Commercial. 

Electricity  for  power  use  will  be  sold,  under  the  following 
scheduTe,  to  any  consumer  who  has  signed  an  agreement  for 
electric  service,  embodying  the  terms  and  conditions  of  the 
company.  "Power"  is  defined  as  general  motor  service,  cook- 
ing, heating,  electroplating,  charging  storage  batteries,  and 
similar  service,  but  does  not  include  the  running  of  dynamos 
for  electric  lighting  purposes. 

A  price  of  12  cents  per  kilowatt-hour  will  be  charged  for 
all  electricity  furnished  under  this  schedule,  with  the  follow- 
ing deductions,  and  the  minimum  charge  will  be  $1.00  per 
month  per  meter:  — 

A  price  of  9  cents  per  kilowatt-hour  will  be  charged  for  all 
electricity  furnished  in  excess  of  23  and  not  exceeding  103 
hours'  use  of  the  *demand  for  each  month. 

*The  demand  is  the  greatest  amount  of  electricity  used  by 
the  customer  at  any  one  time.  Until  such  time  as  the  company 
installs  one  or  more  indicators,  automatically  to  determine  the 
demand,  either  in  whole  or  in  part,  it  may  estimate  the  demand. 
The  demand  on  any  circuit,  when  an  indicator  is  installed,  will 
be  the  average  of  the  regular  monthly  readings  of  the  indicator, 
between  October  1st  and  the  following  February  1st  in  each 
year.  The  demand  so  determined,  beginning  February  1st  of 
each  year,  shall  be  the  demand  for  the  next  twelve  months, 
except  that  the  demand  in  no  case  shall  be  less  than  1/3  of  the 
highest  reading  during  the  previous  twelve  months  and  in  no 
case  shall  be  less  than  one  kilowatt;  and  provided  that  if  any 
direct-connected  elevator  (as  defined  by  the  company)  be  in- 
stalled the  demand  shall  not  be  taken  at  less  than  10  kilowatts. 
The  customer  has  the  privilege  of  having  the  indicator  cut  out 
one  night  in  each  month,  provided  a  48-hour  written  notice  is 
given  to  the  company. 


166  THE   WATTHOUR    METER 

A  price  of  6  cents  per  kilowatt-hour  will  be  charged  for  all 
electricity  furnished  in  excess  of  103  hours'  use  of  the  demand 
for  each  month. 

Whenever  that  portion  of  a  customer's  bill  which  is  cal- 
culated at  the  9-cent  and  6-cent  rate,  or  both,  exceeds  $10.00 
per  month,  a  discount  of  70  per  cent  will  be  allowed  on  such 
excess  over  $10.00. 

Whenever  a  customer's  bill,  after  the  foregoing  deduc- 
tions have  been  made,  exceeds  $100.00  per  month,  a  discount 
of  30  per  cent  will  be  allowed  on  all  in  excess  of  $100.00. 

Elevator  Rates — Commercial. 

Electricity  for  direct  connected  elevator  use  will  be  sold, 
under  the  following  schedule,  to  any  customer  who  has  signed 
an  agreement  for  electric  service,  embodying  the  terms  and 
conditions  of  the  company.  A  "direct-connected  '  elevator  is 
denned  as  being  an  elevator  running  in  guides,  and  in  which 
the  car  starts  at  the  same  time  as  the  motor. 

A  price  of  12  cents  per  kilowatt-hour  will  be  charged  for 
all  electricity  furnished  under  this  schedule,  with  the  follow- 
ing deductions,  and  the  minimum  charge  will  be  $1.00  per 
month  per  meter:  — 

A  price  of  5  cents  per  kilowatt-hour  will  be  charged  for 
all  electricity  furnished  in  excess  of  300  kilowatt-hours  and  not 
exceeding  600  kilowatt-hours  per  month. 

A  price  of  3  cents  per  kilowatt-hour  will  be  charged  for  all 
electricity  furnished  in  excess  of  600  kilowatt-hours  and  not 
exceeding  4000  kilowatt-hours  per  month. 

A  price  of  2,y2  cents  per  kilowatt-hour  will  be  charged  for 
all  electricity  furnished  in  excess  of  4000  kilowatt-hours  per 
month. 

Yearly  Lighting   Rates — Commercial. 

Electricity  for  any  use  will  be  sold,  under  the  following 
schedule,  to  any  customer  who  has  signed  an  agreement  for 
yearly  electric  service,  embodying  the  terms  and  conditions 
of  the  company. 

A  price  of  $60.00  per  year,  payable  in  equal  monthly  install- 
ments will  be  charged  per  kilowatt  of  the  *demand  up  to  and 
including  15  kilowatts. 

"The  demand  is  the  greatest  amount  of  electricity  used  by 
the  customer  at  any  one  time.  Until  such  time  as  the  company 
installs  one  or  more  indicators,  automatically  to  determine  the 
demand,  either  in  whole  or  in  part,  it  may  estimate  the  demand, 
but  in  no  case  shall  it  be  taken  at  less  than  2/10  of  a  kilowatt. 
The  demand  on  any  circuit,  when  an  indicator  is  installed,  will 
be  the  greatest  reading  of  the  indicator  between  November  1st 


RATES  167 

and  the  following  February  1st  of  each  year,  and  the  demand 
so  determined,  beginning-  February  1st  of  each  year,  shall  be 
the  demand  called  for  by  the  agreemnt  for  the  next  twelve 
months,  except  that  the  demand  in  no  case  shall  be  less  than  1/3 
of  the  highest  reading  during  the  previous  twelve  months.  The 
customer  has  the  privilege  of  having  the  indicator  cut  out  one 
night  in  each  month,  provided  a  48-hour  written  notice  is  given 
to  the  company. 

A  price  of  $36.00  per  year,  payable  in  equal  monthly  in- 
stallments, will  be  charged  per  kilowatt  of  the  demand  for  all 
kilowatts  exceeding  15  and  up  to  and  including  55. 

A  price  of  $30.00  per  year,  payable  in  equal  monthly  in- 
stallments, will  be  charged  per  kilowatt  of  the  demand  for  all 
kilowatts  exceeding  55. 

These  prices  do  not  include  the  supply  of  electricity. 

A  price  of  5  cents  per  kilowatt  hour  will  be  charged  for  all 
electricity  furnished  under  this  agreement  up  to  and  including 
1500  kilowatt-hours  per  month. 

A  price  of  3  cents  per  kilowatt-hour  will  be  charged  for  all 
electricity  furnished  under  this  agreement  exceeding  1500 
kilowatt-hours  and  up  to  and  including  5500  kilowatt-hours  per 
month. 

A  price  of  2^  cents  per  kilowatt-hour  will  be  charged  for 
all  electricity  furnished  under  this  agreement  exceeding  5500 
kilowatt-hours  per  month. 

Permanent  Electric  Rates. 

Electricity  for  any  use  in  specified  premises  will  be  sold, 
under  the  following  schedule,  to  any  customer  who  has  signed 
an  agreement  for  at  least  50  kilowatts  of  permanent  electric 
service,  embodying  the  terms  and  conditions  of  the  company. 

A  price  of  $60.00  per  year,  payable  in  equal  monthly  in- 
stallments, will  be  charged  per  kilowatt  of  service  up  to  and 
including  15  kilowatts. 

A  price  of  $36.00  per  year,  payable  in  equal  monthly  in- 
stallments, will  be  charged  per  kilowatt  of  service  for  all 
kilowatts  exceeding  15  and  up  to  and  including  55. 

A  price  of  $30.00  per  year,  payable  in  equal  monthly  in- 
stallments, will  be  charged  per  kilowatt  of  service  for  all 
kilowatts  exceeding  55. 

These  prices  do  not  include  the  supply  of  electricity. 

A  price  of  5  cents  per  kilowatt-hour  will  be  charged  for 
all  electricity  furnished  under  this  agreement  up  to  and  includ- 
ing 1500  kilowatt-hours  per  month. 

A  price  of  3  cents  per  kilowatt-hour  will  be  charged  for 
all  electricity  furnished  under  this  agreement  exceeding  1500 


168  THE   WATTHOUR   METER 

kilowatt-hours  and  up  to  and  including  5500  kilowatt-hours  per 
month. 

A  price  of  iy2  cents  per  kilowatt-hour  will  be  charged  for 
all  electricity  furnished  under  this  agreement  exceeding  5500 
kilowatt-hours  and  up  to  and  including  105,500  kilowatt-hours 
per  month. 

A  price  of  1*4  cents  per  kilowatt-hour  will  be  charged  for 
all  electricity  furnished  under  this  agreement  exceeding  105,- 
500  kilowatt-hours  per  month. 

The  company  will  deliver  its  electricity  at  the  customer's 
premises,  and,  in  consideration  of  not  supplying  lamps  and 
care,  will  deduct  from  the  net  amount  of  the  bill,  as  otherwise 
rendered,  y2  cent  per  kilowatt-hour. 

The  company  will  provide  capacity  for  intermittent  over- 
loads up  to  40  per  cent  in  excess  of  the  kilowatts  applied  for 
by  the  customer. 

An  excess  price  of  20  cents  per  kilowatt  hour  will  be 
charged  for  all  electricity  furnished  at  any  time  in  excess  of 
the  kilowatts  applied  for  by  the  customer. 

Terms   and    Conditions. 

For  the  purpose  of  determining  the  amount  of  electricity 
used,  a  meter  shall  be  installed  by  the  company  upon  the  cus- 
tomer's premises  at  a  point  most  convenient  for  the  com- 
pany's service,  upon  the  reading  of  which  meter  all  bills  shall 
be  calculated.  If  more  than  one  meter  is  installed,  unless 
for  the  company's  convenience,  each  meter  shall  be  consid- 
ered by  itself  in  calculating  the  amount  of  the  bill.  When 
more  than  one  meter  or  discount  indicator  is  installed  under 
this  agreement,  for  the  company's  convenience,  the  sums 
of  the  consumptions  and  demands  shall,  in  all  cases,  be  taken 
as  the  total  consumption  and  demand. 

All  bills  shall  be  due  and  payable  upon  presentation  and 
shall  be  rendered  monthly,  unless  either  the  customer  or  the 
company  desires  bills  rendered  weekly,  in  which  case  it  may 
be  done  by  adjusting  to  a  weekly  basis  all  the  monthly  figures 
referred  to  in  the  schedule  of  rates. 

A  minimum  charge  will  be  made  of  $1.00  per  month  per 
meter,  unless  otherwise  provided. 

The  customer  will  be  responsible  for  all  charges  for  elec- 
tricity furnished  under  this  agreement  until  the  end  of  the 
term  thereof  and  for  such  further  time  as  he  may  continue 
to  take  the  service;  except  that  where  the  customer  has  the 
right  to  terminate  the  agreement  by  notice,  which  shall  be  in 


RATES  169 

writing,  he  shall  remain  liable  for  all  charges  for  ten  days 
thereafter. 

The  customer  will  be  responsible  for  all  damage  to,  or 
loss  of,  the  company's  property  located  upon  his  premises 
unless  occasioned  by  the  company's  negligence. 

The  company  shall  not  be  responsible  for  any  failure  to 
supply  electricity,  or  for  interruption  or  reversal  of  the  sup- 
ply, if  such  failure,  interruption  or  reversal  is  without  de- 
fault or  neglect  on  its  part. 

The  company  reserves  the  right  to  install  a  circuit 
breaker,  so  arranged  as  to  disconnect  the  service  in  the 
premises,  if  the  company's  capacity  at  that  point  is  exceeded. 

If  a  customer,  who  is  not  paying  a  rate  calling  for  an 
annual  fixed  cost,  desires  to  use  the  electric  service  as 
auxiliary  to  another  source  of  power  (excluding,  however, 
small  sources  of  power  not  exceeding  two  horsepower)  he 
may  do  so  only  by  paying  a  minimum  charge  of  $3.00  per 
month  per  kilowatt  for  as  many  kilowatts  as  it  is  possible  for 
him  to  use  on  the  service  at  any  one  time;  this  number  to  be 
determined  by  a  circuit  breaker,  so  arranged  as  to  discon- 
nect the  service  if  the  number  of  kilowatts  is  exceeded. 

If  lamps  and  care  are  supplied  under  this  agreement, 
they  will  be  supplied  only  for  such  installation  as  uses  the 
company's  electricity  exclusively. 

It  is  agreed  that  all  lamps,  plugs,  meters  and  such  other 
appliances  as  are  furnished  by  the  company  shall  remain  its 
property.  And  it  is  further  agreed  that  all  wiring  upon  the 
premises  of  the  customer,  to  which  the  company's  service  is 
to  be  connected,  shall  be  so  installed  that  the  company  may 
carry  out  this  contract,  and  shall  be  kept  in  proper  condition 
by  the  customer. 

Permission  is  given  the  Company  to  enter  the  custom- 
er's premises,  at  all  times,  for  the  purpose  of  inspecting  and 
keeping  in  repair  or  removing  any  or  all  of  its  apparatus 
used  in  connection  with  the  supply  of  electricity,  and  for  said 
purpose  the  customer  hereby  authorizes  and  requests  his 
landlord,  if  any,  to  permit  said  company  to  enter  said 
premises. 

The  benefits  and  obligations  of  this  contract  shall  inure 
to  and  be  binding  upon  the  successors  and  assigns,  survivors 
and  executors  or  administrators  (as  the  case  may  be)  of  the 
original  parties  hereto,  respectively,  for  the  full  term  of  this 
contract. 


170 


THE   WATTHOUR    METER 


Birmingham  (Alabama)  Railway,  Light  &  Power  Co. 

The  consumer  hereby  agrees  to  pay  the  company,  monthly, 
within  ten  days  after  presentation  of  bills,  for  said  incan- 
descent light  service  at  the  base  rate  of  twelve  cents  per 
kilowatt  hour,  as  measured  by  meter  or  meters  to  be  furnished 
and  installed  by  the  company,  subject  to  the  following  dis- 
counts : 

LIGHTING    RATES. 


On  monthly  bills  under 
"  "      over 


25  k.w.h.  10 


25 

150 

250 

400 

500 

1,000 

1,500 

2,000 

2,500 

3,000 

3,500 


% 


40      % 


45  % 
47V2% 
50  % 


The  consumer  agrees  to  pay  the  company  a  net  minimum 

monthly  bill  of  ( $ )    Dollars  as 

•a  readiness  to  serve  charge. 


POWER    RATES. 

Discount  for  Monthly  Usage. 
500 — 1000    k.w.h.    per    month    10%    discount 

1000 — 2000         "           "  "         12% 

2000 — 3000         "  "         14% 

3000 — 4000         "           "  "         16% 

4000 — 5000          "            "  "         18% 

Over    5000         "  "         20% 

In  addition — 

10  to   15  k.w.h.  used  per  h.p.  installed     4%  discount 

15 —    20        "            "         "        "  "              6% 

20 —    25        "  "              8% 

25 —    30        "            "         "        "  "            10% 

30 —    35        "            "         "        "  "            12% 

35—    40        ' "             14% 

40 —    45        "  "             16% 

45—    50        "             "         "        "  "             18% 

50—    55        "  "             20% 

55 —     60        "             "         "        "  "             22% 

60 —     65        "             "         "        "  "             24% 

€5—    70        "            "         "        "  "            26% 

70 —    75        "            "         "        "  "            28% 

75 —    gO        "            "         "        "  "            30% 

80—    85        "            "         "        "  "            32% 

85 —    90        "            "         "        "  "            34% 

90—    95        "            "         "        "  .  "            36% 

35  —  100        "            "         "        "  "            38% 

Over  100        "            "         "        "  40% 

10%  additional  for  off  peak  service. 


RATES 


171 


The  San  Francisco  Gas  &  Electric  Co.,  of  San  Fran- 
cisco, Cal. 

Lighting    Rates. 

All  current  delivered  to  the  consumer  shall  be  registered 
by  a  meter  or  meters  installed  and  owned  by  the  Company 
and  the  rate  and  minimum  charge  shall  be  as  follows  per 
meter: 


per 


6% 
6 


i* 

4% 
4% 


k.w.h. 

cents    if  the  monthly  consumption  be  less  than 

from 


k.w.h. 

79 

go—  129 
130 —  189 
190—  244 
245 —  309 
310—  374 
375—  449 

550—  674 
675—  849 
850—1099 
1100  or  over 

The  consumer  agrees  to  pay  the  company  a  net  monthly 
minimum  bill  of  $1.00  for  each  meter  installed,  provided  the 
bill  for  current  consumed  at  the  above  premises,  does  not 
equal  or  exceed  the  said  sum  of  $1.00  per  month. 

The  consumer  further  agrees  to  pay  a  minimum  of  $1.50 
per  month,  for  each  horsepower  in  motor  or  motors  installed, 
provided  the  bill  for  current  consumed  does  not  equal  or  ex- 
ceed the  said  sum  of  $1.50  per  horsepower  per  month. 

Power    Rates. 

All  current  delivered  to  the  Consumer  shall  be  registered 
by  a  meter  or  meters  installed  and  owned  by  the  Company 
and  the  rate  and  minimum  charge  shall  be  as  follows  per 
meter: 


Per  1000 
9        cents 

8.55 

8.1 

7.65 

7.2 

6.75 

6.3 

5.85 

5.4 

Per  k.w.h. 

5.25  cents 

5 

4.75 

4.50 

4.25 

4 


If  the  monthly  consumption 
I.  above  the  minimum  and  \  '«• 
shall  be  from  2,000  to  3,000  w.h.  per  16  c.p.  lamp. 
"         '         "       3,000  to  4,000 
4,000  to  5,000 

5,000  to  6,000 

6,000  to  7,000 

"         '         "       7,000  to  8,000 

8, 000  to  9, 000 

"         '         "       9,000  or  over 

If  the  monthly  consumption 
shall  be  from      375  to     649  k.w.h. 

650  to     924 

"    '   "          925  to  1,199 

1,200  to  1,474 

"       1,475  to  1,749 

"        "       1,750  or  over 


172  THE   WATTHOUR   METER 

The  consumer  agrees  to  pay  to  the  company  a  net 
monthly  minimum  bill  of  $1.00  for  each  meter  installed,  pro- 
vided the  bill  for  current  consumed  at  the  above  premises 
does  not  equal  or  exceed  the  said  sum  of  $1.00  per  month. 

The  consumer  further  agrees  to  pay  a  minimum  of  $1.50 
per  month,  for  each  horsepower  or  fraction  thereof  in  motor 
or  motors  installed,  provided  the  bill  for  current  consumed 
does  not  equal  or  exceed  the  said  sum  of  $1.50  per  horse- 
power or  fraction  thereof  per  month. 

From  the  data  given  above,  a  very  good  general 
idea  can  be  gained  of  the  fixing  and  application  of 
lighting  and  power  rates  throughout  the  United  States, 
though  of  course  local  conditions  may  cause  a  wide 
variation  from  the  figures  given. 


APPENDIX. 
Definitions. 

In  many  respects  electric  circuits  closely  resemble 
a  water  system,  in  which  the  pressure  is  analogous  to 
the  voltage  of  the  electric  circuit  and  the  quantity  (in 
cubic  feet  per  second)  to  the  current  flowing  in  the 
wires.  This  comparison  will  often  aid  in  the  solution 
of  various  electrical  problems. 

Definitions. 

Ampere=the  unit  of  electrical  current,  and  is  that 
current  which  will  deposit  silver  at  the  rate  of  o.ooiiiS 
grams  per  second  when  flowing  through  an  electrolytic 
solution  of  silver  nitrate. 

Ohm=the  unit  of  resistance,  and  is  equivalent  to 
the  resistance  of  a  column  of  pure  mercury,  at  o°  cen- 
tigrade, 103.6  centimeters  high,  of  uniform  cross  sec- 
tion, and  weighing  14.4521  grams. 

Volt=the  unit  of  electrical  pressure  (electro- 
motive-force), and  is  that  pressure  which  will  maintain 
the  flow  of  one  ampere  of  current  against  the  resist- 
ance of  one  ohm. 

Let  R=the  resistance  of  a  given  circuit,  E  the 
voltage  impressed  and  I,  the  current  in  amperes,  then 
for  direct  current, 

E  =  R  X  I   (Ohm's  Law), 

which   is  the   fundamental   equation   of  direct  current 
circuits. 

Watt=the  unit  of  electrical  power;  the  watts 
equal  the  product  of  the  volts  and  the  amperes  in 
direct  current  circuits,  and  to  the  product  of  the 
volts,  the  amperes  and  the  power  factor  in  alternating 
current  circuits.  (See  Chap.  II.) 

Kilowatt=one  thousand  watts. 


174  THE   WATTHOUR    METER 

Watthour=the  unit  of  electrical  energy,  and  is 
equivalent  to  the  flow  of  one  watt  for  one  hour. 

Kilowatt-hour=one  thousand  watt  hours. 

Inductance :  The  inductance  of  an  electrical  circuit 
is  the  property  of  that  circuit  whereby  it  can  convert 
electric  energy  into  magnetic  energy,  and  vice  versa. 
Inductance  bears  a  close  resemblance  to  "inertia"  in 
mechanics,  and  has  been  called  "electrical  inertia." 
Inertia  is  that  property  of  a  moving  body  whereby  it 
resists  any  change  in  its  velocity  ;  if  a  rapidly  moving 
body  is  suddenly  stopped,  as,  for  example,  a  hammer 
striking  a  nail,  a  great  force  is  exerted  by  the  body 
against  the  obstacle  which  brings  it  to  rest ;  the  mag- 
nitude 'of  the  force  depending  upon  the  suddenness 
with  which  the  moving  body  is  stopped  and  upon  the 
inertia  of  the  body.  In  an  electric  circuit  containing 
inductance,  if  the  current  is  suddenly  interrupted,  a 
high  e.m.f.  is  produced  which  tends  to  cause  the  cur- 
rent to  continue.  The  magnitude  of  this  "induced" 
e.m.f.  depends  upon  the  suddenness  with  which  the 
current  is  interrupted  and  upon  the  inductance  of  the 
circuit.  The  inertia  of  any  given  body  is  proportional 
to  its  mass ;  the  energy  stored  in  a  moving  body  is 
W  =  T/2  MV2,  where  M  is  the  mass  (=  weight  divided 
by  the  gravitational  constant),  and  where  V  is  the 
velocity.  The  magnetic  energy  stored  in  an  electric 
circuit  due  to  its  current  and  inductance  is  W  =  ^2  LI2, 
where  L  is  the  inductance  and  I  is  the  current. 

Henry=unit  of  inductance ;  a  circuit  having  an  in- 
ductance of  one  henry  will  have  an  e.m.f.  of  one  volt 
induced  in  it  by  a  current  changing  at  the  rate  of  one 
ampere  per  second. 

Milli-henry=o.ooi  henry. 

Power  Factor=the  ratio  of  true  watts  to  apparent 
watts  (see  Chap.  II). 

Cycle — one  complete  wave  or  alternation  of  cur- 
rent or  e.m.f.  (See  Fig.  — ,  Chap.  II.) 

Frequency=number  of  cycles  per  second. 


APPENDIX  175 

Impedance=the  vector  sum  of  the  resistance  and 
the  reactance  of  an  electric  circuit  and  is  expressed  by 
the  following"  equation  : 

Z  =  V  R2  +  X2, 

in  which  R  is  the  resistance  in  ohms,  and  X  is  the 
reactance  (=  2  TT  i  X  L,  where  f  is  the  frequency  in 
cycles  per  second  and  L  is  the  inductance  in  henrys). 
The  voltage  drop  in  an  alternating  current  circuit  con- 
taining both  reactance  and  resistance  is 

E  =  ZX  I, 

where  Z  is  the  impedance  as  above  expressed  and  I  is 
the  current  in  amperes. 

Determination  of  Temperature  Rise  by  Resistance 
Method. 

In  testing  electrical  machinery  such  as  generators, 
motors  and  transformers,  it  is  impossible  to  obtain  the 
internal  temperature  of  the  windings  by  use  of  ther- 
mometers ;  the  following  formula  will  therefore  be  use- 
ful in  determining  the  average  temperature  of  such 
windings : 

rFl         \ 
-  1  IdegreesC, 


in  which  238  is  a  constant ;  R  is  the  initial  resistance  of 
the  winding  at  a  room  temperature,  t,  and  F  is  the  final 
resistance.  If  the  room  temperature  differs  from  25°  C, 
the  calculated  temperature  should  be  corrected  by  l/2% 
for  each  degree  C.  Thus  with  a  room  temperature  of 
15°,  the  rise  in  temperature  should  be  increased  by 
5%,  or  if  the  room  temperature  is  35°,  the  rise  in  tem- 
perature as  calculated  should  be  decreased  by  5%,  etc. 

Adjusting  Meters  for  Use  With  Current  and  Potential 
Transformers. 

The  usual  method  of  testing  watthour  meters  used 
with  current  and  potential  transformers  is  to  test  and 
adjust  the  meters  without  the  transformers,  taking  into 
consideration,  of  course,  the  ratio  of  the  transformers. 
Where  a  great  degree  of  accuracy  is  not  required,  this 


176 


THE   WATTHOUR   METER 


procedure  will  answer  very  well ;  but  where,  as  with 
large  consumers,  a  small  percentage  error  represents  a 
considerable  sum  of  money,  the  errors  introduced  by 
the  current  and  potential  transformers  should  be  taken 
into  account  and,  as  far  as  may  be,  compensated. 

The  errors  introduced  by  the  current  and  potential 
transformers  are  (i)  errors  in  ratio  of  the  transformers 
and  (2)  errors  due  to  improper  phase  relations  between 
the  primary  and  secondary  currents  and  e.m.f's. 

The  errors  due  to  ratio  can  be  easily  compensated 
by  adjusting  the  meter  in  accordance  with  the  ratio 
curves  of  the  transformers  at  unity  power  fatcor.  The 
ratio  of  the  potential  transformer  will  remain  constant 
as  its  load  is  constant.  The  ratio  of  the  current  trans- 
former will  not  remain  constant,  but  will  vary  with  the 
load.  It  tends  to  make  the  meter  fast  at  full  load  and 
slow  at  light  load.  This  can  be  compensated  by  ad- 
justing the  meter  to  be  a  little  slow  at  full  load  and  fast 
at  light  load. 

The  errors  due  to  improper  phase  relations  be- 
tween the  primary  and  secondary  currents  and  e.m.f.'s 
are  of  more  serious  nature  and  more  difficult  to  elim- 
inate than  errors  due  to  ratio.  The  errors  from  this 
source  are  negligible  at  unity  power  factor,  but  may  be 
considerable  at  low  power  factors,  depending  on  the 
design  of  the  transformers. 

The  diagram,  Fig.  I,  shown  below,  is  a  vector  dia- 
.gram  of  a  current  transformer.  OI  is  the  primary  or 


Fig.  1. 


APPENDIX 


177 


line  current,  OI'  is  the  secondary  current  and  lags  be- 
hind OE',  the  secondary  e.m.f.  of  the  current  trans- 
former, by  an  angle  depending  on  the  power  factor  of 
the  secondary  load  (meter  coils  and  leads).  II"  is  the 
exciting  current,  the  magnetizing  component  of  which 
is  at  right  angles  to  and  the  energy  component  in 
phase  with  the  primary  e.m.f.,  OE,  of  the  current  trans- 
former. OI"  is  that  component  of  the  primary  current 
inducing  a  current  in  the  secondary,  or  is  the  second- 
ary referred  back  to  the  primary.  It  will  be  seen  that 
OI'  leads  OI  by  and  angle  a  which  will  tend  to  make 
the  meter  run  fast  on  inductive  loads. 

Fig.  2  is  the  vector  diagram  of  a  potential  trans- 
former. OE  is  the  primary  e.m.f.  OE'  is  the  secondary 
e.m.f.  OI  is  the  primary  current,  OF  the  secondary 


Fig.  2. 

current  and  IF  the  exciting  current.  E"N  is  the  e.m.f. 
consumed  by  resistance  or  is  the  RI  drop,  EN  the  e.m.f. 
consumed  by  the  reactance  or  is  the  XI  drop,  and  EE' 
is  the  impedance  e.m.f.  of  the  transformer.  In  the  fig- 
ure it  will  be  seen  that  the  secondary  e.m.f.  (OE"  re- 
ferred to  the  primary)  leads  the  primary  e.m.f  by  an 
angle  a'.  This  will  tend  to  make  the  meter  run  slow  on 
inductive  loads. 

Obviously,  if  a  of  the  current  transformer  equals  a 
of  the  potential  transformer  there  will  be  no  error  from 
this  source,  and  it  is  attempted  in  the  design  of  meter 
transformers  to  approximate  this  condition.  For  this 
reason  considerable  resistance  is  introduced  into  the 


178  THE   WATTHOUR   METER 

potential  transformer  to  increase  this  angle.  This  high 
resistance  results  in  a  transformer  of  poor  regulation, 
but  the  regulation  is  not  important,  as  the  load  is  con- 
stant and  the  range  recommended  narrow. 

In  practice,  the  angle  a  of  the  current  transformer 
is  greater  than  the  angle  a  of  the  potential  transformer. 
This  difference  can  be  compensated  in  the  lag  of  the 
meter.  Suppose,  for  example,  the  meter  is  not  lagged 
properly  by  the  angle  <o.  Then,  if  a  —  a  —  a>  =  O  there 
will  be  no  error  from  this  source.  In  other  words,  the 
meter  is  lagged  so  that  it  will  run  slow  on  inductive 
loads.  The  combined  effect  of  angular  displacement 
in  the  potential  transformer  and  of  the  meter  not  being 
lagged  quite  ninety  degrees  just  compensates  for  the 
angular  displacement  of  the  current  transformer. 

These  angles  may  be  determined  and  corrections 
made  as  follows :  The  results  obtained  by  this  method 
:are  sufficiently  accurate  for  adjusting  service  meters 
since  finer  corrections  could  not  be  made  on  the  meters 
themselves. 

With  an  indicating  wattmeter  the  power  flowing 
in  a  circuit  of  50  per  cent  power  factor  (or  other  known 
power  factor)  is  read.  A  one  to  one  ratio  current 
transformer  of  the  type  used  with  the  watthour  meters 
is  then  inserted  in  the  circuit  and  the  current  for  the 
watt-meter  is  taken  from  the  secondary  of  the  current 
transformer.  The  power  is  again  read.  Assuming  that 
a  power  factor  of  50  per  cent  is  used,  from  the  first 
reading  we  get  W  =  El  cos  60°  and  from  the  second 
reading  W  =  El  cos  (60  —  a).  The  angle  a  is  the 
angular  displacement  due  to  the  current  transformer. 
From  the  above 

W  cos  60° 

COS    (60  —  a)    = 


W 

From  which  we  can  readily  obtain  a.  Before  substitut- 
ing in  the  formula  W  should  be  corrected  for  error  in 
transformer  ratio.  The  current  coils  of  the  watt-meter 
are  again  connected  directly  in  circuit  and  the  potential 
supplied  by  potential  transformers,  two  transformers 


APPENDIX 


179 


being  used,  one  to  step  up  from  the  line  voltage  and 
the  other  to  step  down  again  to  the  watt-meter.  We 
can  now  obtain  the  angular  displacement  due  to  the 
potential  transformers  by  applying  the  same  formula 
as  given  above  for  current  transformers.  The  angle 
thus  obtained  for  the  potential  transformers  will  be 
twice  the  angle  of  one  transformer,  and  as  it  is  the 
angle  of  one  transformer  with  which  we  are  concerned 
the  result  obtained  should  be  divided  by  two.  This  will 
give  us  the  angle  a'.  We  will  then  lag  the  meter,  not  for 
90°,  but  for  90°-  -  (a  —  a'). 

Another  and  quicker  way  of  applying  this  method 
is  to  determine  the  error  introduced  by  two  potential 
transformers  at  unity  and  at  50  per  cent  power  factor. 
Each  transformer  is  responsible  for  ^  of  the  error. 
Now  connect  the  watthour  meter  in  circuit  with  the 
current  transformer  and  with  two  potential  trans- 
formers, one  potential  transformer,  stepping  up 
from  the  line  voltage  (testing  circuit)  and  the 
other  stepping  down  to  the  watthour  meter.  The 
indicating  watt-meter  should  be  connected  di- 
rectly in  the  circuit  without  current  or  potential 
transformers.  The  watthour-meter  is  than  adjusted  at 
unity  power  factor  and  at  50  per  cent  power  factor  to 
disagree  with  the  indicating  watt-meter  by  the  amount 
of  the  error  due  to  one  potential  transformer.  There 
will  be  errors  due  to  three  transformers,  one  current 
and  two  potential.  The  wratthour-meter  is  to  operate 
with  but  two  transformers  and  should  be  adjusted  to 
compeiir'vte  for  the  errors  of  only  two  transformers. 
By  not  compensating  for  the  error  of  one  of  the  poten- 
tial transformers,  as  outlined  above,  the  desired  results 
will  be  accomplished. 

It  is  not  strictly  correct  to  take  l/2  the  error  of  the 
two  potential  transformers,  as  outlined  above,  as  the 
error  of  one  transformer;  it  is,  however,  very  close, 
closer  than  adjustments  can  be  made  on  the  watthour- 
meter. 


INDEX 


Accuracy,   equation  and  per  cent, 
127,  128,  139. 

factors  affecting,  3,  5. 

induction  meter,  curve  of,  43. 

initial,  3. 
Adjustments,  139,  30,  175. 

commutating  meters,  70,  75. 

for  friction,  6. 

polyphase  meter  elements,  6i 
Ampere,  definition,  173. 
Ampere-hour    meters     (see    mer- 
cury flotation). 

Armatures,    commutating    meters, 
72. 

astatic  arrangement,  82. 

open-circuited,  153. 


Backward  rotation,  induction  me- 
ters, 116. 

commutating  meters,  153. 
Balance,  three-wire  systems,  78. 
Balance  loop,  induction  meters,  61. 
Bearings,  upper,  9,  154. 

construction,  lower,  4,  10. 
Brushes,  71. 


Calibration,  curves  of,  43,  147,  148. 
Capacity,  selection  of,  7,  115. 

overload,  7. 

Commutating    meters,    alternating- 
currents,  75. 

adjustments,  70,  75. 

armature  construction,  72. 

armature,  open  circuits  in,  153. 
astatic  arrangement  of,  82. 

backward  rotation,  153. 

brushes,  71. 

commutator,  71,  153. 

comparison  to  shunt  motor,  66. 


Commutating  meter,  compensating 
field,  70. 

constants  (see  testing). 

construction,  general,  68. 

efficiency,  68. 

four  pole  type,  83. 

heating  of  frames,  8. 

lagging,  75. 

switchboard  type,  80. 

temperature  coefficient,  74. 

three  wire  type,  77. 

parts,  74. 

principle  of  operation,  65. 
Compensating  field,  70. 
Connection    diagrams,    commutat- 
ing type,  83  to  86. 

indicating  instruments,  18  to  22. 

2  single  phase  meters  on  3  wire 
single  phase  circuit,  44. 

2  single  phase  meters  on  4  wire 

2  phase  circuit,  46. 

2  single  phase  meters  on  3  wire 

3  phase  circuit,  46,  50,  53. 

3  single  phase  meters  on  4  wire 
3  phase  circuit,  54. 

3  single  phase  meters  on  6  »hase 

circuit,  57. 

single  phase  3  wire  meter,  44. 
single  phase  meter  with  3  wire 

transformer,  45. 

1  polyphase  meter,  3  and  4  wire 
circuits,  60. 

2  polyphase  meter  on  6  phase 
circuits,  62. 

3  phase,  4  wire  meter,  58. 
manufacturer's     diagrams,     spe- 
cial note,  64. 

measurement  of  power,  15  to  23. 

mercury  meter,  94. 

metering  high  potential  circuits. 

63. 

Constants  (see  testing). 
Construction,  general,  7. 
Covers,  7. 

Creeping,  6,  38,  152. 
Current  transformers    (see  trans- 
formers). 


182 


INDEX 


Definitions  (see  Appendix  also),  1. 
Demand  indicators,  100. 
Diagrams   (see  connections). 
Discs,  troubles,  152,  154. 

construction  and  material,  10. 
Distributing  system,  losses  in,  2. 
Duncan  meter,  68,  124. 

E 

Efficiency,  high,  meters,  68. 

low,  meters,  68,  14. 
Elements,  adjustments  of,  61. 

interference  of,  62. 


Formulae  (see  testing). 

Fort  Wajme  meters,  adjustments, 

30,  36. 

constants,  122,  123,  127,  128. 
Frames,  7. 
Frequency,  effect  of  variations  of, 

39  to  43. 

Frequency,  definition  of,  174. 
"Friction  torque,"  6. 


Gear,  worm,  9. 

ratio,  120. 

General    Electric    meters,    adjust- 
ments, 30,  33. 

constants,  119,  120,  127,  128. 
Glass     covers,     reasons     for     not 

using,  8. 

Grounding    secondaries    of    trans- 
formers, 63. 

H 

Heating    of  frames,   commutating 

meters,  8. 

Henry,  definition  of,  174. 
Humming    of    induction     meters, 

151. 


Impedance,  definition  of,  175. 
Inductance,  definition  of,  174. 
Induction  meters,  adjustments,  30, 

33,  36,  37,  39,  61,  175. 
accuracy  of  (calibration  curve), 

43. 
backward  rotation  of,  116. 


Induction  meters,  used  as  balanced 
load  indicator,  52. 

"balance  loop,"  61. 

calibration,    curve    of,    43,    147, 
148. 

connections    of    (see   connection, 
diagrams). 

constants  (see  testing). 

creeping,  causes  of,  38. 

double  lagging,  33,  39. 

elements,  interference  of,  62. 

Fort  Wayne,  adjustments  of,  30, 
36. 

Fort   Wayne,  constants  of,  .'122, 
123,  127,  128. 

frequency,  effect  of  variation  of, 
39  to  43. 

General  Electric,  adjustments  of, 
30,  33. 

General    Electric,    constants    of, 
119,  120,  127,  128. 

humming  of,  151. 

interference  of  elements,  62. 

lagging,  28,  33,  39. 

light  load  adjustment  device,  33, 
36,  37. 

Vector  diagram  of,  29. 

parts  of  (illustration),  35. 

polyphase  type  of,  58. 
4  wire  type,  58. 

power  factor,  influence  of,  28. 
adjustment  devices,  30. 
determination,  by  use  of,  55. 

principle  of  operation,  24. 

reasons  for  extensive  use  induc- 
tion type,  24. 

single  phase  meters,  advantages 
of,  53. 

single    phase    meters    on    poly- 
phase circuits,  45  to  58. 

single   phase    meters    on    unbal- 
anced 3  phase  circuits,  49. 

speed  of,  121. 

standard    meters     on   old   volt- 
ages, 54. . 

3  wire  type,  44. 

Westinghouse,    adjustments    of, 
30,  37. 

\Vestinghouse,  constants  of,  121, 

127,  128. 

Indicators,  demand,  100,  104. 
Installation,  114,  116. 
Inspection  records,  116. 
Interference    of    elements,     poly- 
phase meters,  62. 


INDEX 


183 


Jewel,  lower  bearing,  4. 
Jewels,  installation  of,  117. 

selection  of,  and  life,  11. 

testing  for  defective,  153. 

K 

Knopp  method  of  testing,  132. 
Knopp    "milli-hour"    stop    watch, 
133. 


Lagging  (see  commutating  type). 
(See  induction  type). 

Leveling,  conventional  method  of, 
115. 

Light  load  adjustment  (see  com- 
mutating induction  meter). 

Lightning,  protection  of  current 
transformers  from,  64. 

Locations  of  meters,  114. 

Losses  in  distributing  system,  2. 


M 


Magnets,  retarding,  5. 

process  of  manufacture,  13. 

weakening  of,  151. 
Maximum  demand  indicators,  104. 
Measurement  of  power,  15  to  23. 
Mercury  flotation  meter,  alternat- 
ing current  type,  92. 

ampere-hour  type,  93. 

direct  current  type,  89. 

connections  of,  94. 

constants  and  testing  (see  test- 
ing). 

principle  of  operation,  87. 


Ohm,  definition  of,  173. 
Overload  capacity,  7. 
Overmetering,  6,  80,  115. 


Percentage  of  error,  equation  of, 

127,  128,  139. 
Pivots,  4. 
Phantom  loads,  130. 


Power  factor,  testing  for  leading 
or  lagging,  132,  141. 

adjustments  for,  28.  29,  30,  75. 

determination  of,  55. 

graphically  represented,  16. 
Power,  measurement  of  (see  con- 
nection diagrams). 

definition  of,  22. 

equations  of,  17. 
Prepayment  meters,  96. 

R 

Rates,  155. 

Ratio,  soecial  potential  trans- 
former, 54. 

Reading,  systems  of,  107. 

Recording  watt-meter,  definition 
of,  1. 

Recording  mechanism,  5,  13,  154. 

Records,  systems  of,  107,  116. 

Register  ratio,  121,  149. 

Revenue,  relation  to  meter  sys- 
tem, 1. 

Rotating  standard,  method  of  test- 
ing (see  testing). 


Sangamo     meters     (see     mercury 

flotation). 

Selection  of  meters,  3,  7,  83. 
Shunt     field     (see      commutating 

meter). 
Shafts,  9,  152. 
Switchboard     type,     commutating 

meters,  80. 


Temperature    rise,     determination 

of,  175. 

Testing  adjustments    (see  adjust- 
ments), 
constants  and  formulae,  Duncan, 

124. 

Fort  Wayne,  122,  123,  127,  128. 
Gen.  Elec.,  119,  120,  127,  128. 
Sangamo,  125. 
Westinghouse,  121,  127,  128. 
equations  of  accuracy,  127,   128, 

139. 

methods    of    indicating    instru- 
ment, 118. 


184 


INDEX 


Testing  for  shop  work,   140. 

Knopp,    132. 

phantom  load  transformer,  130. 

rotating  standard,  125,  128. 

special  portable  set,   137. 

polyphase  meters,  144. 

records,  113. 

Three   wire   meters,   commutating 
type,  77. 

induction  type,  44. 
Three  wire  system,  balance  of,  78. 
Torque,  value  of  high,  4. 
Total  output  meters,  80. 
Transformers,  current,   errors  of, 
145,  175. 

calibration  curve  of,  147. 

double  primary,  45. 

grounding  of  secondaries,  63. 

loads  imposed  upon,  64. 

protection  from  lightning,  64. 
Transformers,  phantom  load,  130. 


Transformers,  potential,  errors    >f, 
148,  175. 

grounding  of  secondaries,  63. 

loads  imposed  upon,  64. 

special  connection  of,  54. 
Troubles,  general,  150. 


Vibration,  methods  of  preventing. 

150. 

(See  installation). 
Volt,  definition  of,  173. 

W 

Watches,     Knopp's     "milli-hour/ 

133. 

Watt,  definition  of,  173. 
Watthour,  definition  of,  174. 
Watthour  meter,  definition  of,  1. 
Worm  gear,  9. 


7  DAY  USE 


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